Sounds to me like it's switching on, but not POSTING.
If that's the case, you'll need to remove the back cover and try taking out the RAM and see if it beeps at you when you turn it on. If it does, re-seat the ram modules one at a time and see if it powers on. If it's still doing the same thing, disconnect the the HDD and DVD drive, and other peripherals that are connected & see what happens then. Let me know.