|Do you see the BIOS post screen ? Or can you boot into BIOS and see the BIOS configuration pages ?|
If no, this seems to be a hardware issue rather than software. When you press the power button, do the fans start rotating and hard disk making noise ?
If this is a desktop, then remove the side cover and start checking with the electrical connections. Also check if there is a missing connection, such as the one to the video card.