Try unplugging everything for a few minutes, let it sit and then plug back up an retry. Sometimes the machine needs a time out.
I have an IS7 motherboard (800 mhz FSB) but have PC3000 Kingston ram. Tonight I (stupidly?) tried changing the bus speed to 667 (or something like that) to run in sync w/the ram, but the computer almost immediately rebooted. When it was restarting it locked up so I held the power button down for a few seconds to power it down. I reset the CMOS by switching the jumper and when I tried turning it back on I get nothing...there is a green light on the Motherboard that is lighting up, all the wires from the case are still connected and the wires on the front power-on button appear to be okay, but it doesn't power on.
I'm kinda desperate here. Any ideas?