help me find the cause of my random reboots

this just started happening yesterday and it has me stumped.specs are all in sig and I am running XPpro sp2.Tuesday I went out and got Star Wars Battlefront and played it for a good 6 hours with no problems.Then yesterday I go to start it up and *BAM* reboot.so I'm thinking hmm my overclock is memtest/prime/3dmark stable but we had turned the AC off and temps had risen about 8c so I lower my overclock and voltage as well as turn the ac back on.same problem.at that point I said lets reinstall a few things and see if that helps so I reinstall DX9c,cat 4.9,audigy drivers,and chipset drivers for good measure.same problem.I then run the hard drive test from western digital on both of my HDD's and they come up clean(0 errors).I have done check disk and again it came up clean.at this point I'm down to thinking it is one of two things,either my psu is going out(tests strong with DMM and the only rail that moves is the 12v from 12.10 to 12.00 at full load) or my windows install is somehow corrupt.
I have checked the error log and the only thing that appears out the ordinary is some error with the sojubus which I googled but came up with very little info.sorry for the long post but I wanted to give as many details as possible.

I would check out this thread for starters:
http://www.ocforums.com/showthread.php?t=265143

Check RAM, PSU and heat.

first thanks for the link.I have checked the psu with a DMM and its solid as a rock.even though I just did a 7 hour 22 loop of memtest last week I just ran another loop just to be sure(passed) so I think the ram is good.the prime/memtest/3dmark tests all were done in the last 10 days as The ram I have is brand new.I thought heat may be the issue as well but didn't want to jump to conclusions as the 8 degree rise in temp only put me in the low 40's at idle and no higher than 48 at load according to the mobo sensors.I forgot to mention that I did some pretty aggresive registry cleaning within the last two days so maybe I corrupted something while I was doing that.

well I found out the problem was a sound card driver conflict.something with the EAX console.anyway I only posted this follow up to help in the fiture if someone actually uses the search function.