Is my Nvidia 8800 GT a dead case?

My PC died 2 days ago.I think it is the grafic card that is broken, again.
I have removed the power connector inside the computer box from the card. I had my computer (HP pavilion d4180) repaired 1 year ago and the power connector cable to the 8800 GT seems to go directly into the power supply( HP made that, dont know if it is a good thing)
I have not disconnected the card from the motherboard. My question is; do I have to disconnect the card from the motherboard and then turn on the PC and se if it works without the card? Or can I leave it connected since the power cable is removed?

I have a 400 watt power supply.I have read on internet that it isnt enough or is it, for the 8800 GT 512 MB, reference card?