X server crashes too frequently

[elhoir]

but i dont know anymore, it crashes with different apps and it is automatically respawned.
Xorg log attached

ProblemType: Bug
DistroRelease: Ubuntu 15.10
Package: xserver-xorg 1:7.7+7ubuntu4
ProcVersionSignature: Ubuntu 4.1.0-3.3-lowlatency 4.1.3
Uname: Linux 4.1.0-3-lowlatency x86_64
.tmp.unity.support.test.0:

ApportVersion: 2.18-0ubuntu9
Architecture: amd64
CompizPlugins: No value set for `/apps/compiz-1/general/screen0/options/active_plugins'
CompositorRunning: compiz
CompositorUnredirectDriverBlacklist: '(nouveau|Intel).*Mesa 8.0'
CompositorUnredirectFSW: true
CurrentDesktop: Unity
Date: Thu Sep 3 01:19:08 2015
DistUpgraded: 2015-07-10 00:03:13,900 DEBUG enabling apt cron job
DistroCodename: wily
DistroVariant: ubuntu
DkmsStatus:
 vboxhost, 4.3.28, 4.0.9-040009-lowlatency, x86_64: installed
 vboxhost, 4.3.28, 4.1.0-3-lowlatency, x86_64: installed
ExtraDebuggingInterest: Yes, if not too technical
GraphicsCard:
 Advanced Micro Devices, Inc. [AMD/ATI] Turks PRO [Radeon HD 6570/7570/8550] [1002:6759] (prog-if 00 [VGA controller])
   Subsystem: PC Partner Limited / Sapphire Technology Device [174b:e193]
InstallationDate: Installed on 2012-02-27 (1283 days ago)
InstallationMedia: Ubuntu 11.10 "Oneiric Ocelot" - Release amd64 (20111012)
MachineType: MEDIONPC MS-7616
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-4.1.0-3-lowlatency root=UUID=cded073e-f845-4947-970b-f8a4290c4c2b ro quiet splash acpi_osi=Linux crashkernel=384M-:128M crashkernel=384M-:128M crashkernel=384M-:128M crashkernel=384M-:128M crashkernel=384M-:128M crashkernel=384M-:128M vt.handoff=7
SourcePackage: xorg
UpgradeStatus: Upgraded to wily on 2015-07-09 (55 days ago)
dmi.bios.date: 01/15/2010
dmi.bios.vendor: American Megatrends Inc.
dmi.bios.version: A7616MLN.10F
dmi.board.asset.tag: To Be Filled By O.E.M.
dmi.board.name: MS-7616
dmi.board.vendor: MEDIONPC
dmi.board.version: 1.0
dmi.chassis.type: 3
dmi.chassis.vendor: MEDIONPC
dmi.modalias: dmi:bvnAmericanMegatrendsInc.:bvrA7616MLN.10F:bd01/15/2010:svnMEDIONPC:pnMS-7616:pvr1.0:rvnMEDIONPC:rnMS-7616:rvr1.0:cvnMEDIONPC:ct3:cvr:
dmi.product.name: MS-7616
dmi.product.version: 1.0
dmi.sys.vendor: MEDIONPC
version.compiz: compiz 1:0.9.12.1+15.10.20150805-0ubuntu1
version.ia32-libs: ia32-libs N/A
version.libdrm2: libdrm2 2.4.64-1
version.libgl1-mesa-dri: libgl1-mesa-dri 10.6.3-1ubuntu1
version.libgl1-mesa-dri-experimental: libgl1-mesa-dri-experimental N/A
version.libgl1-mesa-glx: libgl1-mesa-glx 10.6.3-1ubuntu1
version.xserver-xorg-core: xserver-xorg-core 2:1.17.2-1ubuntu4
version.xserver-xorg-input-evdev: xserver-xorg-input-evdev 1:2.9.2-1ubuntu1
version.xserver-xorg-video-ati: xserver-xorg-video-ati N/A
version.xserver-xorg-video-intel: xserver-xorg-video-intel 2:2.99.917+git20150808-0ubuntu2
version.xserver-xorg-video-nouveau: xserver-xorg-video-nouveau N/A
xserver.bootTime: Thu Sep 3 01:18:31 2015
xserver.configfile: default
xserver.devices:
 input Power Button KEYBOARD, id 6
 input Power Button KEYBOARD, id 7
 input USB 2.0 PC Camera KEYBOARD, id 8
 input Chicony Chicony wired mouse MOUSE, id 9
 input AT Translated Set 2 keyboard KEYBOARD, id 10
xserver.errors:
 Failed to load module "ati" (module does not exist, 0)
 Failed to load module "ati" (module does not exist, 0)
xserver.logfile: /var/log/Xorg.0.log
xserver.version: 2:1.17.2-1ubuntu4
xserver.video_driver: modeset