new system = random freeze

[Deller]

Hi
just build the following system and i'm seemingly random freezes (BLACK screen of death)

PSU: Be Quite 750w (from old system)
RAM: 4gb (4x1) OCZ DDR3 14400
CPU: E8500
GFX: Ati 3870x2
hdd1: 74gb raptor (boot)
hdd2: 36gb raptor (from old system)
hdd3: 36gb raptor (from old system)
mobo: Asus P5E3 Premium wifi

Vista oem m. sp1

After 1. install everything seemed fine, system ran great, 3dmark06 ran fine.
Then i startet installing games:
World in conflict = crash
C&C+Kane's wrath = crash

sometimes during loading screen, sometimes after 1 or 2 hours play.

after a couple of crashes and consequent resets the system started acting "wierd"
it would now sometimes crash while surfing aswell.

Did a fresh install yeasterday, everything was fine till i installed gfx driver and wanted to set my
res. to 1680x1050 = system rebooted, what the....

latest bios installed (had to dig out an old pci card to be able to update it (black screen))
ran memtest86 for 2 hours without errors
ran the memtest thing of the Vista dvd , no errors

So now i'm really lost and don't know where to look for errors

EDIT
link to pic with temps. , this is 2min after boot, the time it took to install everest and grab the screen.
GPU2 temps seem a bit high ? and now that i think about it i don't think iv'e heard the fan speed up expect for 3-4secs during POST

also: the 2 switches on the 3870, what are they for ?

http://metaldetektor.googlepag...g/temps-full;init:.jpg

 

[Deller]

update:
borrowed a radeon x1950xt pci-e card, ran kane's wrath for about 5mins no problem
ran 3dmark06 with no problems (scored 6364)

then i wanted to try kane's wrath again = machine froze during load screen....FRAK

During the 06 test i did notice a high pitch noise in between tests, mosfet/capacitor ?

So , either the mobo or visat suck ?