Just completed my first PC build. After a few minor hurdles, everything was running brilliantly, OS and all drivers installed, basically finished the process. All that was left to do was tidy up the wires in the case, which involved disconnecting and reconnecting some of the cables to get them into suitable positions (The only other change I made was to plug in 2 extra case fans).

When I booted up after doing this, no fans were spinning, so I turned off power almost immediately. Unfortunately, it may have been too late as there was a smell of smoke coming from somewhere.

I checked all the power connections, and nothing seemed obviously wrong (though it's possible that something wasn't quite in) and also disconnected the two fans I had just connected (basically aiming to put things back to their last working state). Now when I turn on power all the fans run fine, but the system doesn't boot. I've tried changing video cards, RAM, and clearing CMOS and none of these have made a difference, so I'm guessing either the PSU, CPU or motherboard is broken, though I don't have sufficient knowledge to tell which, nor do I have compatible spares of any of them to interchange.

Other information which may be relevent: The blue LED on the mobo still works when power is on, there are also two other LEDs labelled cr12j2 and cr12j3 which turn on when I try to boot, amber and green respectively.

The hex Post code displayed on the mobo just shows "--" and doesn't change.

All fans work (does this mean it isn't the PSU?), though the LEDs on the PSU fan dim significantly a couple of seconds after power up, which did not happen before the problem occured.

Specs:
BFG nForce 680i Sli mboard
Intel Q6600 cpu
OCZ GameXstream psu

These are all the details I can think of. Can anyone give me an idea of where the problem may lie, or failing that any suggestion of how I could determine the problem.

Strip the system down to the bare minimum. Disconnect the power & data cables from all drives (HDD, optical, floppy), remove all cards except video, remove all but one stick of RAM, unplug all the case fans, unplug all external devices except keyboard & monitor. Now see if you can bootup & access the BIOS.

Done, but no luck. The system behaves exactly as before.

Given what I've said, is it possible to rule out any out of the cpu, psu and motherboard as the faulty component?

Can you smell a burnt or smoke smell in the psu?

Have you tried putting in another psu?

If putting in another psu doesn't work then your motherboard is prob fried.

If something smelled burned then it propably was. Look for melted wires or discoloration. My guess would be the PSU. Did you have the unit unplugged from the wall while tidying up?

I kept it plugged in but turned off at the psu. Someone suggested going over the board with a magnifying glass to find discoloration (like you said) and I did find a chip which appeared to be burnt out.

Image here: http://img504.imageshack.us/img504/...

I'm going to replace the mobo, and I'm also exhanging the psu for one I know works, just in case a fault in the psu lead to the problem in the first place. Hopefully that will solve the problem, we'll see.

Thanks to everyone who gave me advice, it's been a big help.

When pulling the MBoard out of the case check to verify that all metal standoffs were in the proper locations, under screw holes, and ONLY in those locations. Also look for foriegn objects in the case. Things like a loose screw. Extra standoffs can cause a short in the MBoard.