M2N-SLI Deluxe - Doesn't Power Up

I attempted to build the following new system: M2N-SLI Deluxe, Athon64 X2 4600+, Crucial DDR2-800 2x1G, XFX 7600GT, PC Power & Cooling TurboCool 510 SLI, WD 160GB SATA HDs (which I intend to run in RAID-1) plus Antec Case, floppy, Plextor DVD-R/RW. (This is the 6th system I've built, but it has been 8 years since the last build.)

My first problem (indicated by 1 long/2 short beeps) was incompatible RAM though Crucial assured me the RAM I got should work with the M2N-SLI Deluxe. Borrowed a 1G Kingston DDR2-533 RAM and got it into the BIOS. Used the BIOS' EZ-Flash 2 utility to upgrade the BIOS from 0202 to 0304. Powered down, replaced the Kingston with the Crucial RAM and powered up. No problems.

Proceeded to configure RAID-1 and install Windows XP Home. After a couple of hours of trying, gave up and turned the computer off for the night (power button, turned off the PSU and unplugged the power cord).

The next morning plugged the power cord back in, turned on the PSU and hit the power button to turn on the computer and nothing. The SB_PWR LED on the motherboard was on. Tried reseting the CMOS RAM. Tried it outside the case. Tried a second CPU (Sempron64 2800+). Tried the PSU from another computer. Tried that computer's TurboCool 300 (not enough to run a whole computer, but enough to at least power up MB, CPU and RAM). Verified the power switch was working. I seem to have ruled out everything but the motherboard.

After several calls to ASUS tech support, they said it would be best to RMA the board with newegg. After a week, the replacement motherboard arrived. Hooked it to the PSU with Crucial RAM and video board. Hit the power button and nothing.

Again tried the PSU in another computer - it worked in that computer. Again tried the TurboCool 300, but this time it actually powered up, but gave the 1 long/2 short beeps, which I expected - just indicated the BIOS needed updating. Powered off using power button, disconnected power cord. But the Kingston RAM in. Unfortunately it would not power up after that with either PSU. Also again tried other CPU, reset CMOS RAM, etc. etc. Nothing excecpt the SB_PWR LED.

Is the motherboard a sleep and I can't wake it?

Now I'm suspecting the PSU. Perhaps it's not compatible with this motherboard or has become incompatible (is was working the first night after updating the BIOS). The TurboCool 510 SLI is suppose to be a quality PSU. Did it go bad somehow? It does still work in an older computer.

Again ASUS tech support could offer nothing (even got to a level 2 tech). So now I'm going to RMA it directly to them using their advance exchange program (they send me a tested and certified board first before returning the bad board).

Since I also suspect the PSU, I'm getting another new PSU (this time an Antec TruPower 510 II). (If it looks like I'm getting enough parts for another computer, you would be right - which is OK because all three desktop computers in our house are more than 6 years old).

Does anyone have any thoughts or ideas?
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