wow, that sounds weird. Sounds like it could be a few of things. It could be the nvidia drivers, it could be the bios settings, it could be xorg, it could be related to power states such as running the cpu @ 800mhz instead of 2.4ghz. Sounds pretty vague.
look at /var/log/kdm.log
~ Y </0 5+Up1</ P30p[Ez +Ry 2 R34</ D1s? ~