unexplainable failure - Please help!

[darkslyde]

i've had this problem ever since i built my rig (about 2 months). it will basically crash randomly - there are 2 types of crash. 1- happens during high-end games like coh, cod4, gears of war etc. the game will freeze, and stutter, and the sound also stutters and the only way to recover control of the machine is to press windows key (if the game allows it) and kill the proc in taskman, or manual restart. and 2.- random crashes, usually in desktop, where the thing will freeze up completely and a high-pitched beep comes out of the speakers; only solution is to manual reset.
now let me talk you through what i've done to try and resolve this. 1) delete partition and reinstall xp. 2) virusscan with norton (clean). 3) new cpu cooler +arctic silver 4) memtest (no errors). 5) replaced my cheap 650w psu (which was meeting rail requirements) with a brand new £100 antec trio 650w, which now reads about -0.5v on each rail (????) 6) saw that the gfxcard and soundcard were sharing an irq, so reseated the sound card to another pci slot, changing its lane. 8 ) repeatedly cleaned and reseated the cards (carefully) 9) did the nvidia NAM removal trick 10) yes, i have the latest nforce drivers 11) flashed BIOS (a last resort).. and there is more that i can't remember now.
i built this machine from scratch and every component was brand new.
xp sp2
dualcore e6850
msi 8800 ultra
asus p5n32-e sli plus
2gig OCZ platinum
x-fi xtreme music
there is NO REASON why it should be messing up like this. and it happens EVERY TIME. i'm sure you can understand how frustrating it is having bought the latest games for my massive rig which can handle them but being unable to actually PLAY them. the only thing i can think of is that the card is faulty.. considering it cost £400 and is now out of returns period that wouldnt be very good. all i'm doing is bleeding money on this machine..it's driving me crazy... please, anyone with any ideas, much appreciated.

[Wally]

I hate new build problems, the best thing you can do (if possible) is to test all your components on another rig. If this is not possible, then your best bet is to take it to your local pc shop and get them to find the fault for you.