geforce 8800gt and vostro 410

Hello everyone

I have trouble with my computer wich is vostro 410 (quad q9450 - 2.66 ghz - 1333 mhz - 12 mb - dual hd  2x500 gb - vista sp1 - nvidia geforce 8800 gt) since i had it.

Computer need to reboot 3 times before opening vista and work normaly.

It look like coming from graphic card cause has i re-started with the geforce disabled it work well running with the incorporated graphic card on the motherboard.

I called the dell french technical support and they send me new one (and also new hdd in same time cause restart everytime = crashed) but it still the same; i have no answer and i'm still waiting for a solution.

As i looked here in the forum i saw that the alimentation for 8800gt need to be more than 400w but my computer is only 300w, is that the point ?

Is anyone can help ?

Sorry for my English , i try my best !

Franck