Over the weekend i succesfully overclock my old 240 from 550 to 650mhz (GPU), and 1012 to 1157mhz (Memory clock) http://files.myopera.com/godsmackerna/albums/4103402/XFX-GT-240X-ZNFC.jpg
The card ran stable through furmark tests, but proven unstable during minecraft gameplay
Pics:
Default: http://imgur.com/t5YD5
Overclock: http://imgur.com/DXjME
Sorry i couldn't get any pics of MC gameplay being funky
Even dropping the card back default setting minecraft was still unstable, flashing weird textures randomly, allowing me to see through the map in certain areas, and flickering particles everywhere.
I'm not too sad i broke this card, as it was used before and i picked it up for $15
Probably not the best of Ideas to OC a entry level card :D Why the hell do you need to OC for minecraft anyway?pretty sure a gameboy color could run that! :)
On a serious note, you can try to uninstall the drivers (Nvidia drivers) in safe mode and reinstall the drivers again and wham bam thank you mam bobs your uncle all is well in the world again.
note: optifine was installed. i could run on far settings, i was only OC'ing it because i have a better card and i wanted to see if i could push my render farther