[edit, on retrospect, your computer locks up altogether so this info doesn't apply to you, but I'll leave it for others who might gain from it]
I'd try to get your hands on a different computer or a different videocard and see if the symptoms persist. I had something similar happen, and it turned out that my Geforce 2 was killing my monitor, probably through incorrect refresh timing. Usually I had to turn the monitor off and back on again to get the picture back, every time I changed resolutions. I bought a geforce 3, and after about a week, I haven't had any of those symptoms with my monitor again, though I'll probably want to send it back before warranty is out because there was definite damage done.