When my system freezes up what I try first is to log into my daughter system and then remotely log into mine and restart the graphics. In the last 3 years I've had only 1 time that my whole system was froze (My own software I was working on). Its usually only the the graphics that freeze. To list what programs that are running in a shell type ps -e. If you type in the word top you'll see what program is using all the cpu process. type q to cntl-c to get out of top.