Whenever I overclock My 8800 GTS, It freezes and just crashes. The temperatures are under 65°C, and I know my PSU is well enough to power the thing. How do increase the voltage on the card?
Can't increase voltages without volt mods/bios flashes. If it's crashing at a very low overclock then it may be clocked as high as the card can go without being unstable.
Take it from me, Oc'ing GPU's gives minimal gains in real performance(usually less than 10 fps with max OC), if you're happy with your cards performance leave it at normal clocks, if not get a new card that will be sufficient for your needs at stock clocks.
ps- Could also be your powersupply failing, OC'ing a gpu increases the power that it draws and if you're almost maxed out before your overclock, overclocking and drawing more power can do you in. This wouldn't be my first guess, but I have seen it before.