CPU not booting ( fans and DVD-drive works fine).?

[tiger]

Ok i was cleaning the CPU fan (one above the processor ) and after reinstalling it back in my system would not boot up. I can see the fan working and even the DVD-drive works but im not getting any display on the monitor. I removed my Nvidea gfx card and even reseated the ROM in the other slot. I tried removing and refitting the fan too. I tested my monitor with my laptop and it works fine.

What might be the cause and how to fix this?.

Specs :
Mother board : DG31PR
RAM : 2 gigs DDR2 (i guess. I bought this about 3 years ago).
Processor : Intel core 2 duo.
80 gig hard-disk.

 

[SuperAnswerer]

Remove the RAM and start the computer. If it beeps, clean the RAM and fit it back in. The computer should work now. If it does not beep, try the same with the BIOS battery.