Ubuntu hangs while boot process

[shadow]

Ubuntu freezes during kernel boot on my Acer TravelMate 5720 Notebook. No ubuntu logo, loading screen etc.
The kernel with this problem is 2.6.32. Via grub I can boot 2.6.31 where the problem does not occur, the PC boots normally.

I can also boot with 2.6.32 kernel, if I set the boot parameter acpi=off

uname -a:
2.6.32-20-generic #29-Ubuntu SMP Fri Apr 9 20:35:55 UTC 2010 i686 GNU/Linux

ProblemType: Bug
DistroRelease: Ubuntu 10.04
Package: linux-image-2.6.32-20-generic 2.6.32-20.29
Regression: Yes
Reproducible: Yes
ProcVersionSignature: Ubuntu 2.6.32-20.29-generic 2.6.32.11+drm33.2
Uname: Linux 2.6.32-20-generic i686
AlsaVersion: Advanced Linux Sound Architecture Driver Version 1.0.21.
AplayDevices:
 **** List of PLAYBACK Hardware Devices ****
 card 0: Intel [HDA Intel], device 0: ALC268 Analog [ALC268 Analog]
   Subdevices: 1/1
   Subdevice #0: subdevice #0
Architecture: i386
AudioDevicesInUse:
 USER PID ACCESS COMMAND
 /dev/snd/controlC0: floyd 1390 F.... pulseaudio
CRDA: Error: [Errno 2] No such file or directory
Card0.Amixer.info:
 Card hw:0 'Intel'/'HDA Intel at 0xfc300000 irq 21'
   Mixer name : 'Realtek ALC268'
   Components : 'HDA:10ec0268,1025011f,00100003 HDA:14f12c06,10250093,00100000'
   Controls : 18
   Simple ctrls : 12
Date: Tue Apr 13 14:25:08 2010
HibernationDevice: RESUME=UUID=3b273b47-61ce-4d6c-b269-a96decc08217
MachineType: Acer TravelMate 5720
PccardctlIdent:
 Socket 0:
   no product info available
PccardctlStatus:
 Socket 0:
   no card
ProcCmdLine: root=UUID=4cd968b9-2289-40dc-8b36-1dd85587a0a7 ro quiet splash acpi=off
ProcEnviron:
 LANG=de_DE.UTF-8
 SHELL=/bin/bash
RelatedPackageVersions: linux-firmware 1.33
RfKill:
 0: phy0: Wireless LAN
  Soft blocked: no
  Hard blocked: no
SourcePackage: linux
WpaSupplicantLog:

dmi.bios.date: 04/15/2008
dmi.bios.vendor: Phoenix Technologies LTD
dmi.bios.version: V1.34
dmi.board.name: Columbia
dmi.board.vendor: Acer
dmi.board.version: Rev
dmi.chassis.asset.tag: None
dmi.chassis.type: 10
dmi.chassis.vendor: Acer
dmi.chassis.version: N/A
dmi.modalias: dmi:bvnPhoenixTechnologiesLTD:bvrV1.34:bd04/15/2008:svnAcer:pnTravelMate5720:pvr0100:rvnAcer:rnColumbia:rvrRev:cvnAcer:ct10:cvrN/A:
dmi.product.name: TravelMate 5720
dmi.product.version: 0100
dmi.sys.vendor: Acer