Not enough power? 6800gt

I recently bought a 6800gt from a forum member so that I could get BF2 running However I have crashes while playing the game where it freezes for a while (along with sound looping) and then the computer restarts afer about a minute of hanging.

I suspect this may be a power problem since I never had any problems before, but now I have this new card thats pulling a lot more than my 4400 did. I have a 400W supply powering whats in my signature. The card runs at a stable temp during the game, so I don't think it is a heat problem.

restarts/freezing is tough to diagnos. What brand power supply is it? If it's a generic I'd say get a new one anyway. Generic power supplies are bad news for an overclocked system. It's like getting a brand new sports car and putting cheap/crappy gas in it. Are you 3dmark stable? Prime95 stable? how long? stable in other games?

PSU is an antec (SL400) and is maybe 3 years old. Honestly I havent run 3dmark or any other games yet, BF2 is the first game ive tried with the new card. Everything has been fine until the new more power hungry card.

I'll try going to stock speed on my cpu and running 3dmark now!