computer won't start to windows, or BIOS

[thquart]

I have a custom built PC. AMD athlon 2700+SD single core processor. EVGA geforce 7600 GS video card. 1024 mb DDR4 ram. DFI lanparty motherboard. seagate7200rpm 80 gig ( i think) HDD.

Last night i tilted my computer and it shut off. I saw that the pwer cord slightly came out of the power source, and plugged it back in. When i turned mypc back on, four red  LED lights at the bottom left of the motherboard went on. Under them is the word "DEBUG". My processor turns on, my video card turns on, my dvdrw drives opens and closes, but nothing more. My monitor on/off light blinks, but i know this isn't the monitor because this has happened before, and i've waited a few minutes, turned it back on and it's been fine. One time i blew some dust out and it was fine. Now, there isn' much dust, everything is plugged in where it's supposed to that i can see, everything seems to be working, but all i get is a black screen. Anyone have any ideas what i can do? thanks.

[2k_dummy]

Shut down, remove and reseat video card. Use ESD precaution.

edit: and reseat ram

[thquart]

I've used two different video cards in the two different PCIE x16 slots i have...i'm getting  the please check signal cable from the monitor now, so at least that's progress.

The pink dots at the very bottomleft indicate where the red lights are. EDIT: the lights are actually right aboce where i indicated, on the little white strip.