Xorg freeze / nvidia-driver-390 does not boot

[igi]

Ubuntu installed in legacy mode (efi not supported)
graphic card: Nvidia GF108 [GeForce GT 520]
Kernel: linux-image-4.15.0-30-generic

With default driver active [xserver-xorg-video-nouveau] the performance is reduced (compared to active nvidia driver in previous 16.04 installation). Running games often leads to screen freeze (hard reboot necessary).

On the other hand proprietary drivers do not work properly:
1) with nvidia-driver-390 the system locks before showing gdm login (bad chars shown) with last kernel;
2) with nvidia-driver-390 the screen is forced to 680x480 res using kernel linux-image-4.15.0-23-generic; also LAN/internet does not work;
3) with nvidia-340 the monitor switches off during boot and the boot does not continue;

Also tried to activate the nvidia ppa (ppa:graphics-drivers/ppa) to try the legacy driver (304), but I can't since it breaks several other packages.

Googling around my guess either is for bugs in kernels from 4.15.0-23 or for signed modules not working without efi.

Thanks for your support!

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: xorg 1:7.7+19ubuntu7.1
ProcVersionSignature: Ubuntu 4.15.0-30.32-generic 4.15.18
Uname: Linux 4.15.0-30-generic x86_64
ApportVersion: 2.20.9-0ubuntu7.2
Architecture: amd64
BootLog: Error: [Errno 13] Permesso negato: '/var/log/boot.log'
CompizPlugins: [core,composite,opengl,decor,regex,compiztoolbox,move,resize,imgpng,place,animation,expo,grid,vpswitch,mousepoll,workarounds,snap,gnomecompat,unitymtgrabhandles,session,ezoom,wall,fade,scale,unityshell]
CompositorRunning: None
CurrentDesktop: ubuntu:GNOME
Date: Sun Aug 12 09:34:04 2018
DistUpgraded: Fresh install
DistroCodename: bionic
DistroVariant: ubuntu
ExtraDebuggingInterest: Yes
GpuHangFrequency: Several times a day
GpuHangReproducibility: Occurs more often under certain circumstances
GpuHangStarted: Since before I upgraded
GraphicsCard:
 NVIDIA Corporation GF108 [GeForce GT 520] [10de:0de4] (rev a1) (prog-if 00 [VGA controller])
   Subsystem: ASUSTeK Computer Inc. GF108 [GeForce GT 520] [1043:83d2]
InstallationDate: Installed on 2018-08-08 (3 days ago)
InstallationMedia: Ubuntu 18.04.1 LTS "Bionic Beaver" - Release amd64 (20180725)
MachineType: System manufacturer System Product Name
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-4.15.0-30-generic root=UUID=6a0b9e44-0c07-4365-bdbb-a6a9ac7f88bd ro quiet splash vt.handoff=1
SourcePackage: xorg
Symptom: display
Title: Xorg freeze
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 08/31/2012
dmi.bios.vendor: American Megatrends Inc.
dmi.bios.version: 1105
dmi.board.asset.tag: To be filled by O.E.M.
dmi.board.name: F1A55-M
dmi.board.vendor: ASUSTeK COMPUTER INC.
dmi.board.version: Rev X.0x
dmi.chassis.asset.tag: Asset-1234567890
dmi.chassis.type: 3
dmi.chassis.vendor: Chassis Manufacture
dmi.chassis.version: Chassis Version
dmi.modalias: dmi:bvnAmericanMegatrendsInc.:bvr1105:bd08/31/2012:svnSystemmanufacturer:pnSystemProductName:pvrSystemVersion:rvnASUSTeKCOMPUTERINC.:rnF1A55-M:rvrRevX.0x:cvnChassisManufacture:ct3:cvrChassisVersion:
dmi.product.family: To be filled by O.E.M.
dmi.product.name: System Product Name
dmi.product.version: System Version
dmi.sys.vendor: System manufacturer
version.compiz: compiz N/A
version.libdrm2: libdrm2 2.4.91-2
version.libgl1-mesa-dri: libgl1-mesa-dri 18.0.5-0ubuntu0~18.04.1
version.libgl1-mesa-glx: libgl1-mesa-glx 18.0.5-0ubuntu0~18.04.1
version.xserver-xorg-core: xserver-xorg-core 2:1.19.6-1ubuntu4
version.xserver-xorg-input-evdev: xserver-xorg-input-evdev N/A
version.xserver-xorg-video-ati: xserver-xorg-video-ati 1:18.0.1-1
version.xserver-xorg-video-intel: xserver-xorg-video-intel 2:2.99.917+git20171229-1
version.xserver-xorg-video-nouveau: xserver-xorg-video-nouveau 1:1.0.15-2