Same problem on my workstation.
I run Kunbutun from 6.04 to 9.4 and now it's freeze under 20min each time.
While I play kids game (supertux) or on internet with java/flash game too.
Hardware
AMD Athlon(tm) XP 3200+
Asus A7N8 on nforce2
GeForce 6600 GT
Software
Linux vonloschz 2.6.28-11-generic
dmesg.txt
lspci-simple.txt
lspci-detail.txt (lspci -vvnn)
nvidia-bug-report.log
Xorg.0.log
** Attachment added: dmesg.lscpi.nvidia-bug-report.xorg.tar.gz
http://launchpadlibrarian.net/26500959/dmesg.lscpi.nvidia-bug-report.xorg.tar.gz
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Computer hard locks randomly with ubuntu