ASUS GeForce GTX 550 Ti OCing

So, this has become a problem, as of recent events.

My brother thought it was smart to take over my PC while I was out and OC the core clock to 1050 MHz (from the standard factory 910 Mhz), memory clock to 2500+ Mhz, and the vcore to 1.5 (from 1.1) on a locked Pegatron Benecia (commence cringe) using ASUS SmartDoctor, ASUS GPU Tweak, and MSI Afterburner (Yes, ALL three) to play some games with "better quality" (his "undeniable" reasoning, which is quite flawed considering games get unstable with OCing the core clock). After getting the drivers to crash, he reset it back to the default clock (900 MHz), again using MSI Afterburner. This did not fix the problems with FPS instability. Now, when I play, I suffer extreme fps drops (from an unbelievable 70-90 fps to 5-15 fps) and this pesters the heck out of me.

My BIOS is locked (which I had coming, buying a factory-built HP... back in '08) so I don't really have any fixes. If you could point me in the right direction at the very least, or provide instructions on how to revert these, it would be much appreciated.

Basic rig:
Intel Core 2 Quad Q8200 @2.33 Ghz (775 Socket)
Peggy Benencia 1.01
6 GB DDR2 RAM @400 Mhz (2x2 GB, 2x1 GB)
NVIDIA/ASUStek GeForce GTX 550 Ti.

This'll probably be the last thing I write for tonight; I'll be back in maybe 7 or so hours.