I ran ubuntu 10.04 LTS on this machine without problem. I now run ubuntu 12.04 LTS 64-bit. I use it as a backup server and test server which means it's on all the time. That's the problem, because as long as I use it, it now works fine after I changed graphic card, but it still freezes when I leave the machine and want to use it again.
What happen? The machine will automatic turn off the screen and lock the screen. So when I come back, I just move the mouse and type in the password and I can use the machine. This is how it works in day time. Often I could even come the next day and it was still working. Usually it happen during weekend when I was away for more than one night, that when I come back the machine had froze. Lately it has happened every night, so that every morning I have come, I had to restart the computer.
How frozen? Well the only way to get the frozen machine alive, was to hard reset it with the power button. Even Alt + SysRq + REISUB did not work.
I have tried to have different program running to see if any program is causing it. But it happens if I don't have any program running or if I have Firefox, Thunderbird, Opera and VirtualBox running.
Psensor to monitor temperatur is running, but I have not found any unusual temperatures. Dropbox is running. I have checked S.M.A.R.T on the two disc in RAID. Both fine. I have now nvidia graphic card, before ATI, no difference for this case.
CPU Intel Core i3 540 RAM 8GB RAID-1 with 2 disc
I have searched the forum, but not found any answer to this question. And I don't know if this is a bug or not, since I have no clue what trigger the freeze. All I know is that when I come back to work, the computer might be frozen.