I built this system:
Case: Alienware Aurora Desktop, newer case with the easy access panels.
Mobo: Foxconn C51xem2aa Nforce 590 sli
GPU: 2 EVGA eGeForce 7900 GTX running in sli mode (512mb)
CPU: Socket AM2, AMD Athalon 64 FX-62 2000 MT/s Hyper Transport
Soundcard:Soundblaster Fatal1ty Pro Series
Memory: (2 )PC2-6400 DDR2 (400MHz) 1GB
HDD: Seagate Sata Barracuda 7200, 250GB
Other: Physx card by Ageia
PSU: PC Power & Cooling #S75QB 750W, 60A
Rom Drive: LG DVDRAM HL-DT-ST GSA-H10L (IDE)
OS: Win XP Pro SP2
Also has the ELC standard lighting system (the one that uses the dim switches)

The PC was running with an open side panel so that if I needed to change anything...I had access, and it was running great. I even played Crysis Warhead with no issues. Was able to shutdown and turn on multiple times with no issues. All leds for the ELC were operational.

I decided that this system was ready to go and so I put the other side panel on which involved the simple molex hookup from the side panel fan to a molex in the system. I then hooked the power plug back in and turned the system back on, the pled and hdd turned on, then to my surprise off and no power. I rechecked my hookups and didn't see anything missing. I tried to power on the system again and pled and hdd flickered and then nothing, no power. Now there isn't any activity with regards to the pled and hdd leds, nothing, no power.

I removed the side panel and the first thing that I noticed was a funny smell.
No power. So then I removed the cmos battery and reinstalled, nada. I then unplugged the main 24 pin power cable/plug from the mobo but left the fans hooked up and plugged the main 24 pin power cable/plug into a psu tester and the fans all turned on and I got that funny smell. I noticed that the -5v was not lit as well as the +3.3v. Being that the main power was not to the mobo and was to the psu tester, I am assuming the smell was coming from the psu.?.

I need some advice as to what to check. I have not had much experience with pc's having funny smells. My initial thought was perhaps the PSU shorted out but before I go crazy thought I would check with PCGuide first. I don't know why hooking up a molex for the sidepanel fan would do anything. It is baffling to me. This is a brand new PSU and it is not some cheapy bestec psu. I was going to try another PSU but didn't want to do anything until I got some more advice. The next thing I was going to do was to remove the heatsink and take a look at the processor to see if anything looked burned up.
Also, I do not have power connector cables blocking any air flow, they are all neatly cable tied.
So if you could give me some advice it would be greatly appreciated!

I'd be more inclined to believe that the side panel fan is the item shorting out...if you didn't have it disconnected after you opened it back up, give that a try.

I have tried to power on the system with the side panel off and fan disconnected and still no power. I tested the main power cable to the psu tester with the side panel/fan off and I got that smell.

Well after inspecting the side panel fan, I noticed that one of the wires on the fan had the plastic coating worn away, exposing wire which was being secured underneath a metal clip. :(

Unfortunately, the mobo is dead. I took everything apart and did a bare bones test and no power, so I'll have to start over again but with a new mobo and fan replacement. I also looked at the cpu area and didn't see any signs of anything being fried, memory looked ok as well.

**sigh** back to the beginning.

Have you tried a different power supply?

I noticed that the -5v was not lit as well as the +3.3v. Being that the main power was not to the mobo and was to the psu tester, I am assuming the smell was coming from the psu.?

If the PSU failed, why are we replacing the mobo?

If the PSU failed, why are we replacing the mobo?
I agree, does the mainboard smell (fan header fried) or is the smell from the PSU?

Have you tried a different power supply?
Yes have tried with another known working psu when I did the bare bones test.

If the PSU failed, why are we replacing the mobo?
With regards to the psu tester showing the +3.3v not lighting, I am thinking my tester is a little flaky because if I jiggle the tester, the light comes on. With 2 of my other known working psu's, it does the same thing. I need to get a new tester, any suggestions? I took the original psu and hooked it up to another mobo and was able to post and get to bios so I am sure the psu is not fried.

I agree, does the mainboard smell (fan header fried) or is the smell from the PSU?
The smell is coming from the mobo, I believe the fan to either the northbridge or the southbridge, I am not sure which one.
Here is a pic:

http://www.virtual-hideout.net/reviews/Foxconn_C51XEM2AA/019.jpg