I'm having a similar problem on my system. Until recently I could force it to work by using 'acpi=off noapic nolapic', but now it will only boot if I unplug all my usb devices, then plug them back in once the kernel has finished booting. Otherwise it will lock up on the 'io scheduler cfq registered'. There's definately been a weird problem with usb in the past few releases of the kernel but now it is even worse. System is an AMD 3800+ X2, ASUS A8N32-SLI Deluxe (nforce4), root installed on a SATA2 drive, usb devices are a Logitech Cordless Desktop S510, a Logitech G7 mouse, a Dell 2405FPW monitor (has a CF/SD/etc reader), and a Logitech Fusion webcamera plugged into the monitor's usb hub as well. Original install was from a beta2 textmode cd and has been dist-upgraded to current. Snippet of dmesg WITHOUT USB DEVICES PLUGGED IN follows this post. I have no way to capture the dmesg of the kernel when it doesn't boot. [ 0.000000] Bootdata ok (command line is root=/dev/sda2 ro quiet splash) [ 0.000000] Linux version 2.6.15-22-amd64-generic (buildd@crested) (gcc version 4.0.3 (Ubuntu 4.0.3-1ubuntu5)) #1 SMP PREEMPT Sun May 7 15:56:20 UTC 2006 [ 0.000000] BIOS-provided physical RAM map: [ 0.000000] BIOS-e820: 0000000000000000 - 000000000009fc00 (usable) [ 0.000000] BIOS-e820: 000000000009fc00 - 00000000000a0000 (reserved) [ 0.000000] BIOS-e820: 00000000000e9b90 - 0000000000100000 (reserved) [ 0.000000] BIOS-e820: 0000000000100000 - 000000007ffb0000 (usable) [ 0.000000] BIOS-e820: 000000007ffb0000 - 000000007ffbe000 (ACPI data) [ 0.000000] BIOS-e820: 000000007ffbe000 - 000000007ffe0000 (ACPI NVS) [ 0.000000] BIOS-e820: 000000007ffe0000 - 0000000080000000 (reserved) [ 0.000000] BIOS-e820: 00000000fec00000 - 00000000fec01000 (reserved) [ 0.000000] BIOS-e820: 00000000fee00000 - 00000000fef00000 (reserved) [ 0.000000] BIOS-e820: 00000000ff700000 - 0000000100000000 (reserved) [ 0.000000] ACPI: RSDP (v002 ACPIAM ) @ 0x00000000000fb520 [ 0.000000] ACPI: XSDT (v001 A M I OEMXSDT 0x01000602 MSFT 0x00000097) @ 0x000000007ffb0100 [ 0.000000] ACPI: FADT (v003 A M I OEMFACP 0x01000602 MSFT 0x00000097) @ 0x000000007ffb0290 [ 0.000000] ACPI: MADT (v001 A M I OEMAPIC 0x01000602 MSFT 0x00000097) @ 0x000000007ffb0390 [ 0.000000] ACPI: MCFG (v001 A M I OEMMCFG 0x01000602 MSFT 0x00000097) @ 0x000000007ffb0400 [ 0.000000] ACPI: OEMB (v001 A M I AMI_OEM 0x01000602 MSFT 0x00000097) @ 0x000000007ffbe040 [ 0.000000] ACPI: DSDT (v001 A0371 A0371001 0x00000001 INTL 0x02002026) @ 0x0000000000000000 [ 0.000000] Scanning NUMA topology in Northbridge 24 [ 0.000000] Number of nodes 1 [ 0.000000] Node 0 MemBase 0000000000000000 Limit 000000007ffb0000 [ 0.000000] Using 63 for the hash shift. [ 0.000000] Using node hash shift of 63 [ 0.000000] Bootmem setup node 0 0000000000000000-000000007ffb0000 [ 0.000000] On node 0 totalpages: 516022 [ 0.000000] DMA zone: 3020 pages, LIFO batch:0 [ 0.000000] DMA32 zone: 513002 pages, LIFO batch:31 [ 0.000000] Normal zone: 0 pages, LIFO batch:0 [ 0.000000] HighMem zone: 0 pages, LIFO batch:0 [ 0.000000] Nvidia board detected. Ignoring ACPI timer override. [ 0.000000] ACPI: PM-Timer IO Port: 0x508 [ 0.000000] ACPI: Local APIC address 0xfee00000 [ 0.000000] ACPI: LAPIC (acpi_id[0x01] lapic_id[0x00] enabled) [ 0.000000] Processor #0 15:11 APIC version 16 [ 0.000000] ACPI: LAPIC (acpi_id[0x02] lapic_id[0x01] enabled) [ 0.000000] Processor #1 15:11 APIC version 16 [ 0.000000] ACPI: IOAPIC (id[0x02] address[0xfec00000] gsi_base[0]) [ 0.000000] IOAPIC[0]: apic_id 2, version 17, address 0xfec00000, GSI 0-23 [ 0.000000] ACPI: INT_SRC_OVR (bus 0 bus_irq 0 global_irq 2 dfl dfl) [ 0.000000] ACPI: BIOS IRQ0 pin2 override ignored. [ 0.000000] ACPI: INT_SRC_OVR (bus 0 bus_irq 9 global_irq 9 high level) [ 0.000000] ACPI: INT_SRC_OVR (bus 0 bus_irq 14 global_irq 14 high edge) [ 0.000000] ACPI: INT_SRC_OVR (bus 0 bus_irq 15 global_irq 15 high edge) [ 0.000000] ACPI: IRQ9 used by override. [ 0.000000] ACPI: IRQ14 used by override. [ 0.000000] ACPI: IRQ15 used by override. [ 0.000000] Setting APIC routing to physical flat [ 0.000000] Using ACPI (MADT) for SMP configuration information [ 0.000000] Allocating PCI resources starting at 88000000 (gap: 80000000:7ec00000) [ 0.000000] Checking aperture... [ 0.000000] CPU 0: aperture @ 9000000000 size 32 MB [ 0.000000] Aperture from northbridge cpu 0 too small (32 MB) [ 0.000000] No AGP bridge found [ 0.000000] SMP: Allowing 3 CPUs, 1 hotplug CPUs [ 0.000000] Built 1 zonelists [ 0.000000] Kernel command line: root=/dev/sda2 ro quiet splash [ 0.000000] Initializing CPU#0 [ 0.000000] PID hash table entries: 4096 (order: 12, 131072 bytes) [ 0.000000] time.c: Using 3.579545 MHz PM timer. [ 0.000000] time.c: Detected 2009.165 MHz processor. [ 14.542287] Console: colour VGA+ 80x25 [ 14.543318] Dentry cache hash table entries: 262144 (order: 9, 2097152 bytes) [ 14.544789] Inode-cache hash table entries: 131072 (order: 8, 1048576 bytes) [ 14.562178] Memory: 2053800k/2096832k available (2131k kernel code, 42644k reserved, 751k data, 180k init) [ 14.622076] Calibrating delay using timer specific routine.. 4021.11 BogoMIPS (lpj=2010555) [ 14.622123] Security Framework v1.0.0 initialized [ 14.622128] SELinux: Disabled at boot. [ 14.622148] Mount-cache hash table entries: 256 [ 14.622238] CPU: L1 I Cache: 64K (64 bytes/line), D cache 64K (64 bytes/line) [ 14.622240] CPU: L2 Cache: 512K (64 bytes/line) [ 14.622243] CPU 0(2) -> Node 0 -> Core 0 [ 14.622250] mtrr: v2.0 (20020519) [ 14.622257] SMP alternatives: switching to UP code [ 14.622492] checking if image is initramfs... it is [ 15.147278] Freeing initrd memory: 6906k freed [ 15.151409] ACPI: Looking for DSDT ... not found! [ 15.164568] Using local APIC timer interrupts. [ 15.214278] Detected 12.557 MHz APIC timer. [ 15.214381] SMP alternatives: switching to SMP code [ 15.214506] Booting processor 1/2 APIC 0x1 [ 15.224753] Initializing CPU#1 [ 15.285098] Calibrating delay using timer specific routine.. 4017.73 BogoMIPS (lpj=2008865) [ 15.285104] CPU: L1 I Cache: 64K (64 bytes/line), D cache 64K (64 bytes/line) [ 15.285106] CPU: L2 Cache: 512K (64 bytes/line) [ 15.285108] CPU 1(2) -> Node 0 -> Core 1 [ 15.285184] AMD Athlon(tm) 64 X2 Dual Core Processor 3800+ stepping 01 [ 15.285191] CPU 1: Syncing TSC to CPU 0. [ 15.285287] CPU 1: synchronized TSC with CPU 0 (last diff -77 cycles, maxerr 525 cycles) [ 15.285294] Brought up 2 CPUs [ 15.285330] Disabling vsyscall due to use of PM timer [ 15.285332] time.c: Using PM based timekeeping. [ 15.285334] testing NMI watchdog ... OK. [ 15.295638] NET: Registered protocol family 16 [ 15.295662] ACPI: bus type pci registered [ 15.295939] PCI: Using configuration type 1 [ 15.299517] PCI: Using MMCONFIG at e0000000 [ 15.300124] ACPI: Subsystem revision 20051216 [ 15.306367] ACPI: Interpreter enabled [ 15.306370] ACPI: Using IOAPIC for interrupt routing [ 15.306877] ACPI: PCI Root Bridge [PCI0] (0000:00) [ 15.306880] PCI: Probing PCI hardware (bus 00) [ 15.311488] Boot video device is 0000:03:00.0 [ 15.311673] PCI: Transparent bridge - 0000:00:12.0 [ 15.311843] ACPI: PCI Interrupt Routing Table [\_SB_.PCI0._PRT] [ 15.331729] ACPI: PCI Interrupt Routing Table [\_SB_.PCI0.PB2P._PRT] [ 15.332256] ACPI: PCI Interrupt Routing Table [\_SB_.PCI0.PCE0._PRT] [ 15.332546] ACPI: PCI Interrupt Routing Table [\_SB_.PCI0.PCE1._PRT] [ 15.332835] ACPI: PCI Interrupt Routing Table [\_SB_.PCI0.PCE2._PRT] [ 15.333132] ACPI: PCI Interrupt Routing Table [\_SB_.PCI0.PCE3._PRT] [ 15.333422] ACPI: PCI Interrupt Routing Table [\_SB_.PCI0.PCE4._PRT] [ 15.334373] ACPI: PCI Interrupt Link [LNKA] (IRQs 16 17 18 19) *10 [ 15.334803] ACPI: PCI Interrupt Link [LNKB] (IRQs 16 17 18 19) *5 [ 15.335234] ACPI: PCI Interrupt Link [LNKC] (IRQs 16 17 18 19) *5 [ 15.335667] ACPI: PCI Interrupt Link [LNKD] (IRQs 16 17 18 19) *0, disabled. [ 15.336102] ACPI: PCI Interrupt Link [LUB0] (IRQs 20 21 22 23) *5 [ 15.336533] ACPI: PCI Interrupt Link [LUB2] (IRQs 20 21 22 23) *7 [ 15.336965] ACPI: PCI Interrupt Link [LMAC] (IRQs 20 21 22 23) *5 [ 15.337404] ACPI: PCI Interrupt Link [LACI] (IRQs 20 21 22 23) *0, disabled. [ 15.337832] ACPI: PCI Interrupt Link [LMC9] (IRQs 20 21 22 23) *0, disabled. [ 15.338271] ACPI: PCI Interrupt Link [LSMB] (IRQs 20 21 22 23) *5 [ 15.338698] ACPI: PCI Interrupt Link [LSA0] (IRQs 20 21 22 23) *11 [ 15.339142] ACPI: PCI Interrupt Link [LSA1] (IRQs 20 21 22 23) *11 [ 15.339651] ACPI: PCI Interrupt Link [LATA] (IRQs 20 21 22 23) *0, disabled. [ 15.339751] Linux Plug and Play Support v0.97 (c) Adam Belay [ 15.339762] pnp: PnP ACPI init [ 15.345382] pnp: PnP ACPI: found 13 devices [ 15.345400] PCI: Using ACPI for IRQ routing [ 15.345403] PCI: If a device doesn't work, try "pci=routeirq". If it helps, post a report [ 15.345517] PCI-DMA: Disabling IOMMU. [ 15.346751] pnp: 00:09: ioport range 0xc00-0xc0f has been reserved [ 15.346754] pnp: 00:09: ioport range 0xd00-0xd0f has been reserved [ 15.346757] pnp: 00:09: ioport range 0xa20-0xa2f has been reserved [ 15.346760] pnp: 00:09: ioport range 0xa30-0xa3f has been reserved [ 15.346953] PCI: Bridge: 0000:00:02.0 [ 15.346954] IO window: disabled. [ 15.346956] MEM window: disabled. [ 15.346958] PREFETCH window: disabled. [ 15.346961] PCI: Bridge: 0000:00:03.0 [ 15.346963] IO window: 9000-9fff [ 15.346966] MEM window: f6700000-f67fffff [ 15.346968] PREFETCH window: disabled. [ 15.346970] PCI: Bridge: 0000:00:04.0 [ 15.346972] IO window: a000-afff [ 15.346975] MEM window: f6800000-fa8fffff [ 15.346978] PREFETCH window: 9ff00000-bfefffff [ 15.346980] PCI: Bridge: 0000:00:12.0 [ 15.346982] IO window: b000-bfff [ 15.346985] MEM window: fa900000-fa9fffff [ 15.346988] PREFETCH window: disabled. [ 15.346990] PCI: Bridge: 0000:00:16.0 [ 15.346992] IO window: disabled. [ 15.346994] MEM window: disabled. [ 15.346996] PREFETCH window: disabled. [ 15.346999] PCI: Bridge: 0000:00:17.0 [ 15.347001] IO window: c000-cfff [ 15.347010] MEM window: faa00000-feafffff [ 15.347013] PREFETCH window: bff00000-dfefffff [ 15.347022] PCI: Setting latency timer of device 0000:00:02.0 to 64 [ 15.347027] PCI: Setting latency timer of device 0000:00:03.0 to 64 [ 15.347032] PCI: Setting latency timer of device 0000:00:04.0 to 64 [ 15.347036] PCI: Setting latency timer of device 0000:00:12.0 to 64 [ 15.347041] PCI: Setting latency timer of device 0000:00:16.0 to 64 [ 15.347047] PCI: Setting latency timer of device 0000:00:17.0 to 64 [ 15.347332] IA32 emulation $Id: sys_ia32.c,v 1.32 2002/03/24 13:02:28 ak Exp $ [ 15.347656] audit: initializing netlink socket (disabled) [ 15.347663] audit(1147549167.596:1): initialized [ 15.347831] VFS: Disk quotas dquot_6.5.1 [ 15.347847] Dquot-cache hash table entries: 512 (order 0, 4096 bytes) [ 15.347894] Initializing Cryptographic API [ 15.347897] io scheduler noop registered [ 15.347908] io scheduler anticipatory registered [ 15.347916] io scheduler deadline registered [ 15.347932] io scheduler cfq registered (continues on...)