PC does not Bootup

I built a PC with following hardware.

SOYO 875PI Dragon 2 Motherboard.
Intel Pentium 4 3.2 GHz CPU
Case with 450W power supply
120 GB Western Digital Hard drive
CCD-RW/DVD ROM combo
Floppy drive
7-in-1 card reader

The system booted fine and I used it for a little while. One fine morning it decided not to boot. The screen remains blank and I don’t hear the beep when I try to boot the system. Also, once I turn the power on from the front switch I cannot turn it off using that switch.

Any help will be greatly appreciated.

Hemant