i have the same issue every 2 months after installing win7 + a new 2gb ddr2 ram: what you should do is the following but after DISCONNECTING your pc from electricity:
1-remove vga card (if you got one installed by you).
2-remove all hdds.
3-remove usb devices.
4-remove dvd + floppy.
6-remove all ram.
7-if there is dust in it try to remove it with soft paint brush including ram sockets.
8-turn on your pc, you should hear beeps now.
9-turn off pc and disconnect it from electricity, and connect your hdd, then turn it on, it should work fine now.
10-add every component after each one, but turn pc off before adding one component after another.
11-try to update bois with the latest version from intel website.
hope it works...