Freezing/Rebooting Problems

Hello, I've had about 3 earlier threads with similiar topics, which all has led to different problems, that ahas been solved, but I still got some problems with comp freezing/rebooting all the time.

Here's my current setup:

Hardware:
Intel LGA 775 Core2Quad Q9400 Non-clocked
2x2Gb RAM kit Corsair Art Nr TW3X4G1333C9DHX
Tagan 800W PSU(with up to 64A output) (Also grounded with the included cable onto a screw on the Mobo)
Asus GTX260 (Running 16 I think)
Asus P5Q3
Cooler Master 932 High Air Flow(Case)
WD 500Gb HDD
Just another Drive, 16x

BIOS:
DRAM Frequency: 1333MHz
Timing: 9-9-9-24
DRAM Voltage: 1.66V

Other Information:
While running Prime95 and a monitorprogram called CPUID, No cores ever have their Temprature over 60Degrees(Celsius)
If might be a cable problem, as it's my first build, something might be wrong, tho it seems to be correct.
During the first formattingprocess of Windows XP on the machine, the Computer froze during the third part of the process(after creating Partitions and after the procedure first aproximated to take 40mins, but usually takes like 10, no idea what it's called)
The machine is running more stable while using 1.66V on DRAM than 1.6, so I am running with 1.66A at the moment.
After a memorytest, the RAM's(as I understood it) was just fine.
THe RAM's is inserted in the Black ports on the Mobo, Called A1 and B1, there's also two orange, A2 and B2, which I havn't tried the stick in yet.

The Problem:
The computer either Reboots or Freezes(Mostly when more than one program is running)

Question:
What could I possibly have done wrong? And how may I Solve it?

Additional Info:
My brother had a similiar problem to mine, mostly when someone stomped the floor or the machine in some way was shaked, although as he got it repaired(he bought it, guarantee used) they said it was a cableproblem and they just changed it, and now it works just fine.


I might have forgot any info that you need to know, but just tell me and I'll tell you


Thanks alot for you wonderful Knowledge!

Regards and many Thanks

Filip

And I think I got all drivers installed aswell

Sorry for theese "after-posts" It's things I remember after that I've wrote the thread

The Cooling is perfect in the case, nothing is too hot as I can see

I plan to reformat the Computer now inca it Might solve my problem with it, although I'll wait until I've got an answer that might solve the problem without reformatting

Thanks again

Also another note, all parts in the machine is new, an bought on the same day

Just another input, Reformatting seems to be the best option, I strictly think this has to do with the Frexing problem during the first installation

The Air circulation inside the Case is good aswell, and the OS in correctly installed

Could it be a OS error? Should I try Win7 32 RC instead?

I have been googling all the day long but I cant find anyone with the same problem as I got, maybe this problem is a rare one? I am glad for any support