With auto-hide enabled for the task bar I've noticed that my PC may hang for up to two minutes after my monitor kicks back on. Disabling it seems to work... so far. If it does occur again then I have no idea. I tried disabling it after searching and seeing this suggestion on google, so this doesn't seem to be just my issue. My Vostro 1500 laptop does it as well. I've also used W7 on two different motherboards and GPUs.