Computer Completely Dead! - No Response to Power On

I just built a system over the weekend, and everything was working fine. Once everything was installed, I decided to move it upstairs, so powered down as usual. No indications of any problem - normal shutdown of XP. I took the unit upstairs, hooked up all the cables, plugged it in, pushed the front power switch...and nothing: no fans, no lights, no nothing...completely dead. I tried several power cables and outlets - nothing. Took it back to its original location - nothing.
So I swapped out the PSU with a similar unit, same response. Pulled the power switch connector off the mobo and reconnected. Removed everything but essential parts. Still absolutely no response. There is absolutely no smell from the PSU. Could it be the power switch? How can I work around it? Any way to jumper the pins on the mobo so that it thinks the switch is on? I'm absolutely baffled here - it went from perfect functioning to nothing with no indications of any problem whatsoever!!

that's a very strange situation. by "power switch" i'm guessing you meant power cable? if not, try a different cable. and if even that fails, the motherboard may have died from unknown causes.

well when u plug in the kettle lead to the PSU and have the socket turned on as well as the PSU you should see lights on the Motherbaord, so if you dont either the lead, PSU or motherbaord is dead

its unlikely its the PSU as you have tried 3 of them, so its either the Lead or the motherbaord, if i were you i would try another kettle lead, if no LED's on the motherbaord lite up still its likely the motherboard

hmm have you no other leads you could just try, may as well u never know, but it does sound like the motherbaord, but i know i had the same problem before and it was my lead.

i know logically if the lead makes another pc work then the lead must work but often computers have a mind of thier own

if that doesnt work then the Motherboard may just be dead,

it's most likely that the motherboard is dead. if you're sure that the power supply you're using works, then it has to be the motherboard. there's no other explanation that i can think of.