Sure power switch header is correctly plugged in (positive to positive, ground-earth to ground-earth)? Personally had mobo's with three-pin power switch headers, as well as two-pin power switch headers (had to make both work with three pin power switch plug and it took a couple tries).

boxpressed wrote:

My main question is whether the power supply should turn on if the only things I have connected to the motherboard are the ATX power connector and the front panel power switch/LED connector. No drives are connected, and there are no cards in the slot. I just want to power up the unit to BIOS using the onboard VGA and a PS/2 keyboard.

Definitely. Even better, remove the button connector and just leave the ATX power connected. Then just briefly short-circuit those pins where you would connect the button, for example touch them both with a flat (not philips) screwdriver, I don't know how it's called in english. This way you'll also exclude the possibility of a button/connection failure, but make sure you touch the correct pins!
If you try this with a 100% working psu and there's nothing else on the motherboard but the cpu, you can safely assume that the m/b is dead. (Although I have to admit that I've seen very few cases where a faulty m/b prevents the psu from turning on, but it has happened).

Thanks to both of you for your replies. I'm pretty sure that the eight-pin header was fit correctly, largely because a missing pin on the MB corresponds to a solid part on the header.

I forgot to mention that I had used a jumper to short the two power pins with no success.

Sounds like a dead MB, unfortunately!