I need help determining what piece of my computer is in need of attention, please see below for the history on the issue, including some workarounds that worked but dont seem to fix the issue.

Specs:
1x Intel E8400 @ 3.0GHz
2x 1Gig OCZ DDR3 PC3-10666 / 1333MHz / Platinum Edition
1x OCZ 600w GameXstreme PSU
1x Intel X48bt2 MotherBoard
1x Asus EAH4850 ATI 512 Vid Card
1x WD Cavier 250gig sata 2 16mb
On Board sound
On Board Lan
2x 17' Dell LCD 1905fp
Windows Vista SP1

History:
All of this is new as of two weeks ago, everything was bought retail except the MB which was Ebay'd as "New in Box". I orignally tried with Windows XP, but have sense gone to vista as part of the trouble shooting.

I have a problem with reboots, no BSOD, no errors i can find, no Event Viewer Entries, and no MB logs(that i can find). The screen goes black, the monitor goes orange, then comes back to green as it boots up normally.

I have seen these reboots randomly, and every single time i try and load Unreal Tournement 3.

Random Events:
-after making a change to Catalyst control center of downgrading AA and AF by one notch and pressing "OK"
-Dureing the Windows XP loading screen, about 5 seconds into it. This has occured multiple times, some times in a row. I have not seen this sense Vista was installed.
-After boot up in XP, and going into the control panel straight away
-Twice at random points while useing the Spore creature creator.
-At a random point while useing the desktop in Vista.

Unreal Tournament 3:
-As the program starts it displays the copyright info, then reboots before the spam of company logo animations occurs.
-Commenting out the logo animations gets me in game, however the moment i click start game it reboots, and i mean the moment, the loading screens comes up but is gone before you could even read a word of it.

I have tried all the Stickied things on the UT3 forums, none of which worked, and the other reboots that act the same cause me to believe its not a UT3 issue, though UT3 is the only repeatable reboot.

I have tried disabling the on board sound, even in bios. I have tried installed an Audigy sound card as well, no change.

The game has been reinstalled multiple times, and patched.

I have used 8.5 drivers that came with the Vid card, 8.6 Hotfix from their site, and finnally the 8.7 recently released. I have cleanly removed them all before installation.

I tried 3Dmark's newest tests, and saw a reboot once at the start of test 3(CPU test), but it completed it successfully 4 times after that one reboot with no changes made.

What DOES work:
-i swapped my ATI 4850, with a freinds Nvidia 8800. And the game worked, i did not see a reboot outside of it while it was in, but the out of game reboots like i said are not repeatable, though they did happen frequently enough.
---the kicker is he put my ATI 4850 in his machine at the same time, and it worked for his UT3 just fine....no tweaks, 8.6 hotfix drivers.

-I upped the Voltage on my Ram a decent amount(at work atm, i can get the exact amount later, but it was a good amount that was still within OCZ's handling quote). This fixed UT3, runs great at the highest possible settings even, however certain maps will load for a bit then reboot the machine dureing the load.

While the ram voltage is a decent work around, i dont believe this addresses the actual issue.

halp

Check the ram timing as well.

Try with 1 stick of ram mybe one is bad.

Run memtest86 on your ram.

1. Make sure to set the ram voltage an timings to the manufacturer's specs. Look them up.
2. Run memtest86+ to test the ram

The Ram Voltage is within the manufacturere's specs, timinigs are as stated as well.

I ran Memtest finnaly, and after an hour and a half (5 complete tests) there were zero errors.

I also noted a new way to make it reboot, playing half life 2, episode 2 on 1680 resolution, with all graphics turned up, it plays about the first 5 seconsd of the "new game" cinamatic footage, then reboots just the same. I tried turning down AA on the settings and got about 2 more seconds into it, turned settings down more....got further, till finnaly i had gone done a resolution and had no AA....and it worked. It even got to the point where i would get a good 45 seconds through before it rebooted.

halp?

Current ram settings are
Refrence Freq = Default
mem Freq = 1333
TCL 7
trcd 7
trp 7
trasmin 20
trfc 60
trrd 4
twr 10
twtr 5
trtp 5
mem Voltage 1.70
command rate = auto
Total mem 2048 MB

Mem Mode = Dual Channel
Mem Channel A
Slot 0: not installed
Slot 1: 1024 MB DDR 1333 SPD 7-7-7-20
Mem Channel B
Slot 0: not installed
Slot 1: 1024 MB DDR 1333 SPD 7-7-7-20

I have tried them in Slot 0, and it was no different.

appreciate all the responses!

i double checked the ram voltage, according to OCZ's site its default voltage should be 1.8, with it extending beyond that for Over clockers.

so i went in to try and up it a bit more, well the MB doesnt offer 1.8, it ofers 1.78, and 1.82. So i chose 1.78 to be safe, and now the computer wont even POST It was late so i havent pop'd the cmos to reset it yet, but at least this sort of points more at the ram.

Whats interesting is if left to "default" settings the motherboardhttp://en.wikipedia.org/wiki/Motherboard sets the ram voltage to somewhere around 1.35v which is way way below....

the only kicker for me is why the games worked fine with my freinds Nvidia card in my machine, and why my ATI card worked fine in his machine on the same games

Anymore advice by all means please!

This may sound strange, but try a different PSU (it is possible to get a bad/partially bad one), even from OCZ. (the 4850 draws more power than the 8800 too)

i have actually tried a different PSU, a freind of mine has a Corsair 600w psu, his machine is the one the card worked in, but we did try going so far as to move his PSU to my computer, and it made no difference. Perhaps the sum of his parts need for power made the difference that allowed it work in his comp? That is to say, it could be that all of my stuff is drawing more power then his or my pSU can really handle at peak times, where as the sum of his parts need for power even with my 4850, comes out ok?

i have new ram inbound atm, got the same thing so i can bump the machine to 4gigs, but also to try first replacing the current ram and see if it continues. At least then i could rule out ram....

PSU, MB, and Video card are harder to rule out though..