Reinstalled Win 7, now has no display

Hi all,
I built a computer back in Feb. and all was well until a couple of months ago. At this point the screen started flashing on and off (saying it was going to sleep, then turning back on, and repeat) until windows started up. Basically it would skip all bios, etc prior to starting windows. Slowly this got worse until there were times when I had trouble actually getting the computer to turn on (computer would turn on, but screen would just flash). Also, all this time the screen and display worked perfectly once I got it to start. I tried everything I could find online...updating drivers seemed to be a big thing and doing things tothe bios at startup. The only thing was, I could not do annything to the bios because the screen would only flash then and I could never actually get to the bios.

I decided to attempt to reinstall window 7 while already in windows figuring that would start the computer from scratch, including all settings. I started the install and left for awhile to let it install. When I came back the screen was flashing again. Since then I have not been able to get it to stop flashing at all. I have plugged the screen into a laptop and it works fine. I then plugged my desktop into the same laptop and used the laptop to switch the screen to the desktop. The screen showed all black, which I assume is why my monitor keeps flashing (it turns on because the computer is on, but goes to sleep because it is only showing black). Anyway, I am all out of ideas and really don't want to get a new computer seeing as this one should be very powerful. Please, if anyone can help it would be greatly appreciated. As of now, I can't even get a single thing to shop up on the screen, yet it stillstarts up with all fans running (including processor and graphics card)and lights on.

Please, if anyone can help it would be greatly appreciated.