You try it with the CMOS Battery?
Turn the Power off
unplugged the Power Cable
Use a flat screwdriver and get the CMOS Battery out...wait 10 seconds and put it back
And turn the system on...
Ok, sry for that question...but you put the cpu fan back on right?
So...unplugged the Graphics card and try it again...if it works download the driver for your Graphics card.
Maybe the CMOS Battery.
Check your connections with an flat screwdriver. I mean, hold on one Pin and touch the other one and find out, wich one is the right...
Thats the old school way