graphics card problem

I recently bought a geforce 5700 le and read about the good overclocking potential of this card. So I installed coolbits via the registry. The default of this card is 250/400, I pressed the optimize settings button and it set it at 325/490 and then tested it. Ooops, didn't expect that to happen, I didn't apply these changes as it's far too high just off the bat so I reset it to default and pressed the no overclock button. I've been testing this card with GTA III, before it was running smooth, now it stammers along with glitches all over the place.
What the hell have I done, as far as I can see I've done nothing really. I tried uninstalling coolbits, re-installing the driver but it's still the same. Any advice would be appreciated.

 

What exactly happened & what are the rest of your computers specs?

 

When I pressed the optimize buton I thought I would be given the option of testing this new setting but instead it tested it automatically. Could the testing of this new setting have caused damage to my card?
Anyway after the test I reset it to default.

mobo: gigabyte GA-8SIML
cpu: P4 1.5
ram: corsair 256mb pc2700
hdd: IBM deskstar 40g
graphics: geforce 5700 le agp*4
o/s windows 2000 pro