I'm having the same problem...let me see if I can add some details.

It started when I would visit websites, and happen randomly. The monitor shuts off, and the power light turns orange, as if it's not recieving a signal, but the computer power light is still on. Turning the monitor off and on does nothing, nor does hitting ctrl-alt-del...the computer doesn't respond to anything, so I restart it. It kept happening randomly, also happened when I used messenger, so I just disconnected the internet. That worked for awhile, but then it started happening anyway, and sometimes right when windows would boot up to the desktop. I updated Spybot search and destroy, Ad-aware, and Norton, and ran them all three, and it hasn't fixed the problem. Any ideas?