My Compaq PC with Ubuntu 12.04 used to work as it should when all of a sudden, the screen (along with the rest of the system) kept either freezing or crashing.
By freezing, the screen keeps stuck where it was. No mouse or keyboard shortcut can get it back to life.
By crashing, the screen shows a blur decomposition of whatever was showing before or, some other times, a black background with a whole pattern of short slopped lines on top (I describe as I am not allowed yet to put up images). No response neither to any shorcut keys.
Manual power off is needed before restarting. Sometimes then, the boot screen shows up distorted with vertically ligned-up whitw dots over the blue background (its a typical HP boot screen). The system won't start nor do nothing. Power off and unplugging is needed to be granted a new try. Sooner or later it restarts and boots normally.
Apparently random, looks though like it happens when massive resources are about to be used: at video/flash web sites (Chrome and Firefox), opening email manager (thunderbird), or just starting up.
All this happened sooo often with Ubuntu 12.04 and 13.10. Now I use a light Lubuntu and Midori as the browser, and it has happened just a couple of times in the past week. Which I can live with...
Anybody got any idea of what the reason can be? Ubuntu vira? Too old (5 years-old) hardware? Too many partitions for dual boot with Windows Vista (which by the way stopped starting up before all this happened on Ubuntu)? Windows vira spread over partitions???