First, measure whether you get voltages on the cables from the psu to the motherboard.
Next for good measure, remove everything - even the ram blocks and the cpu - from the motherboard.
Check the jumpers up against the manual - make sure everything is set up right.
reset bios (remove battery, move jumper, move jumper back, put battery back)
put one ram block back in, and also the cpu.
Put the graphics card back in.
Attach the psu, and see if you can get a boot (do the cpu fan start rotating when you turn on the psu?)
If nothing happens, try with the other memory block (was there two blocks, or only one?)