+12V dropping on a 520HX

About two months ago I built a new PC with the following components.

Antec P180 case

Asus Crosshair motherboard

XFX GeForce 7950GT 512MB video card

2 x Corsair XMS Dominator 1GB DDR2 800 memory

AMD Athlon 64 X2 5200+ Windso 2.6GHz CPU

Scythe Andy Samurai Master CPU cooler

Western Digital Caviar SE16 500GB SATA Hard Drive

NEC DVD r/rw optical drive

Corsair 520HX power supply

The computer worked great for about a month, but then started getting occasional BSOD physical memory dumps that would freeze, never actually dumping the memory. After rebooting I found that my SATA drive would not be detected, but after waiting 15 minutes or so it would reappear. The frequency of this began to increase and seems to parallel the ambient temperature of the room increasing, so I figured that something was overheating. I added and rearranged fans to increase the cooling of the hard drive and the south bridge of the motherboard without improving the issue.

I removed the physical memory cache from the hard drive to at least stop the physical memory dump from occurring and the other day I finally got another clue on the issue. After the computer rebooted, without the BSOD, a bios warning came up and after checking it out I discovered that my +12V was reading at 9.8v!

After giving it time to cool down and rebooting I checked the voltages again with SpeedFan and the +12V was around 10.5v and dropping. I can chart it as it goes down and it is pretty constant, until it gets too low to apparently run the hard drive and then the system crashes. With a 20c ambient room temperature it will last for a few hours, but if it gets up to 30c then I am lucky to get fifteen minutes. With summer almost here, and the computer in an un-air conditioned room, I doubt it is going to be usable for much longer.

It seems to me at least that this is a faulty power supply, but before returning it I wanted to see if anyone had any other ideas or if this has happened to anyone else.

I have attached an image of SpeedFan showing the voltage dropping over a 45 minute period with an ambient temperature of 25c

Please use the software provided by the MB maker (PC-Probe) and check it with that software. Also what does it say in the Bios?

Turning on the computer, after being off for ~8 hours, and going directly into the bios setup it gave the +12v at 10.94v. After a crash the bios shows it as under 10v.

PC Probe shows the same voltage as Speedfan. A new set of readings, from PC Probe, is as follows

windows login 10.62v

windows login +10 minutes 10.3v

windows login +20 minutes 10.18v

windows login +30 minutes 10.11v

about an hour later the computer crashed.

I have since attached (with tape) a fan to the outside of the power supply to try and pull more hot air out of exhaust grate, but this has not had much effect. The voltage has dropped from 10.6v to 10.18v over 40 minutes.