Check the basics.
Have you tried it with everything unplugged except the first ram dim? (remove video card, other ram, unplug the HDs)
Is the case power lead connected to the motherboard?
Is the reset jump connected correctly?
Are any of the front panel switches stuck in the down position?
Is your powersupply connected to the motherboard?
Is your powersupply connected to your video card?
Are the power cables full inserted in to the back of the computer and monitor?
Are the power cables full inserted in to the wall?
Are the ram dimms fully inserted?
It is one of the basics.