Low 3.3 voltage on motherboard

I have been having the usual reboot problems with Guild Wars. Sometimes it would work for hours, sometimes for a few minutes before rebooting.
Now my computer reboots even when I am not in Guild Wars.
I have noticed in the bios that instead of having 3.3 volts, I have about 2.7 volts. Is this a power supply problem? I've used this 500 watt power supply for about 1 1/2 years with no problems until I installed Guild Wars.

AMD Athlon 64 3000+, not overclocked
w/Stock Cooling Fan, Arctic Silver thermal paste
Sapphire Radeon 9800XT 128 mb
Asus K8ne-deluxe Mobo Nforce 3 chipset
Windows XP sp1 (also tried with SP2)
1 gig Kingston memory
onboard sound
Arctic cooler w/arctic silver thermal paste on video card

To further confuse the problem, Guild Wars runs perfectly on my other computer which is:

AMD Athlon Barton 2600+, overclocked to a 3100
Asus A7n8e-deluxe nforce 2 chipset
Windows 2000 Pro
ATI Radeon 9600 w/256 mb
512 mb Kingston memory
on board sound

Anyone have any suggestions?

put a tester on it and find out what you are really getting.

software will not screw up your voltage as the power supply is too dumb to know it is being diddled

it should still be under warranty so check with tech support on the power supply

The powersupply is "probably" the source of the problem. I had the same problem as you with a P4 2.26 Ghz.

I had 2 identical computers (one for me, one for wife...heh). Mine pooped out on me, got a reading of 1.37v on channel 1 and 7 of the ATX. Wifes computer had 3.3v steady. My machine wouldn't even POST, hers was just fine.

To test your theory, swap the powersupplies for a bit on your two computers and see if the rebooting goes along with the switch. If it does... problem solved

The good thing about it? Powersupplies are cheap, I bought a 430w Antec to replace my dead one for $35 on sale. That was over two years ago.

EDIT: As Loviator suggests, check the warranty also. They may RMA the powersupply for you and all it'll cost is a few bucks shipping!