Not over until the Geek speaks. Some details missing.
Make and model of the motherboard.
What kind of Graphics adapter? Make ad model and type.
Some AGP cards cards stop the motherboard.
Do the keyboard lights flash? How many times?
Normally most DVD drives will let you open the drive is power is applied.
With power off, you can try thins:
Remove cables from board. Remove power for all drives.
(Bad cables and bad drives stop everything.)
Remove RAN.
Remove all USB devices. All devices.
With case open, power up and observe fans. All fans should come on.
Thee ought to be a beep, even three beeps. (No RAM.)
Still not sign of life? If not, the motherboard is now the prime suspect.