What should I do when Ubuntu freezes?
I have a file server that was Windows Home Server. I reformatted the HD and installed Ubuntu 12.04 LTS and Amahai (greyhole, sickbeard, etc) System was working fine but for a while now it randomly freezes up, sometimes a white screen, sometimes vertical lines, sometimes black. I restart it and everything boots up fine, no issues.
All the hardware was recently working with no problems, did memory test, no problem. Ubuntu install with Amahai, fine for a week or so. I don't know if there were any auto updates, only possible changes I can think of. I already googled and disabled hibernate, screensaver, etc. and any other common crashes. When it crashes, I can't access any samba shares or ssh into it.
Where should I look to start to diagnose this issue?