Yeah, many games uses Physx (on ps3 and xbox 360 as well) but only a hand full of games actually use hardware accelerated physx with added particle effects or other simulation effects as result.
Gpu physx game list
Sorry I had to ask about the power supply, having a too weak one will cause errors and crashes etc. Yours is far above what's needed so thats good.
It could be the drivers at fault, I've been using latest beta version 275.50 and I've had no stability issues. You should try changing to different driver, see if it helps any. Be sure to use the option to completely remove the old driver from the system when installing new ones.