OK, I've spent an hour on the search engines, but no luck yet. I accidentally told Vista Business 64 to 'sleep' instead of 'power down'. Now when I try to reboot, only fans run and the CD drive LED blinks a few times: no BIOS, no USB keyboard LEDs/response, no USB mouse LED/response, nothing on the monitors, not even an LED on the power button. I've also tried swapping the positions of the 2 RAM sticks, unplugging the HDs, putting in the Vista DVD on boot, leaving it physically disconnected from the wall for >5 mins - nothing.
HW is Asus P5Q SE mobo, MSI Radeon R4670 graphics, 4GB RAM. As far as I know (I can't get anything out of the computer now), drivers and BIOS were reasonably up-to-date, had no problems for the past month.
Any clues? I need to do some work on that computer, I'm on a co-worker's computer right now!
Remove the battery and reset the CMOS jumper. Instructions are in the MB mnual. Updating to the latest BIOS version may fix the system 'sleep' malfunction. Check for a BIOS version on the product page that adresses the issue.