Why does my computer go to no signal?

i i recently received my 8800gts back from a RMA submission. When i got it back the first thing i did was reformat and install the latest drivers. the card was artifacting right out of the box. also now my computer is randomly going to a “no signal” state. i believe windows is still running is the background bacause i can still hear music in the background, i hold the power button to turn it off. i emailed my power supply company and they told me to reseat my graphic card, which i did but i am still having that problem. I am sure its not my monitor beacuse it works for hours on my other computer without problems. I beleave its a video card problem, but before i start a RMA i wanted to do as much as i can at my home. If there is anything i should try it would be very appreciated. Also Muchkin, my power supply said that because my computer never completely turns off just goes to” no signial” that it couldnt be a problem with my power supply does this seem correct?

The power supply runs everything so if the fan is working etc. the power supply is doing something. If the monitor lights up but goes to a color chart and says no signal , there is no connection to the PC.
Plugs in wrong place or video card problem or something shut down the PC
Pull the plug out of the video card on the PC and see if that changes anything on the Monitor. Narrow down the problem that way.

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