overclocked gpu problem

Hello,
i have a palit gtx 460 1gb 192 bit factory overclocked 778/2004/1556,some times i get random crashes in many games, and
some times screen freeze's while gaming with weird colors green yellow......,i had to restart the pc to make it run normally,
i have installed the latest driver version 304.78 bita what should i do, down-clock the gpu to a normal 460 gtx stock clocks 675/1800/1350 ?
psu cooler master 600w

you dont have to down clock all the way to stock just nudge it down a little til you can get it stable.