Lately, I have noticed that my monitor screen suddenly goes into what looks like a tv set screen when there is no channel selected- what some people call snow on the screen. It's not a frozen pattern, and it is all over the screen. It has happened a few times in the past few weeks. Turning the monitor off and on immediately corrects the problem, and it doesn't happen again for days. Does this sound like it could be the monitor or the graphics card? Thanks for any advice.