If the issue persists after you try Frilock's recommendation, there is a fairly decent chance that there is a physical problem with your hardware. There's still a chance that it might be a big that NVidia hasn't patched yet, or maybe an OS bug, but the odds that it is hardware related go up significantly at this point.
---------- Post added at 18:51 ---------- Previous post was at 18:43 ----------
The lack of a reboot makes the issue significantly different. It's much more likely to be an Orbiter issue, somewhat less likely to be a driver issue, and much, much, much less likely to be a hardware issue than the OP. You should post a separate thread to make sure that it gets proper attention.