Just assembled new computer... reboots every 5 sec... HELP

[Flipparn]

Built a new system...

MSI P45 Platinum Mainboard (MS-7512 v1.1)
Intel E8600 Core Duo CPU
Coirsair Twinx 4GB
GeForce GX2 Gfx
Northq Black Magic 850W PSU (NQ-4775-850-FLEX)

Connected PSU main power cable to MB, + the atx 12v to mainboard, and on poweron, the computer lights up and fans spin for 1 second.. then it shuts off, then 3-4 seconds later.. it tries to start again. It keeps going like this until I pull the powercable out of PSU. Thats my problem.
Switched from a 8pin ATX 12v cable to a 4pin ATX 12V cable. (Mobo has 8 pins but had a cover for 4 of them default)
Still same issue.

Tried to install my old 500W PSU just to see if mobo is working.
That PSU online have 4pins ATX12V cables.. so could only put a 4pin in there... and mobo starts and boots up ok (had no gfx card in at the time since that psu dont have to right conectors for it. Needed 1 8pin + 1 6pin power cable for it.

Then I noticed that on the big powercable goin to mainboard (24pins I think) the pin#20 was missing.. was no cable there.. hmm?
Called the support from company I bought the stuff in and they said its supposed to be missing pin 20. Im confused. My old PSU had a #20
In mainboard manual it only said "Pin 20 - RES" Is that reset? is it resetting all the time? Restore?
Is my new PSU faulty? Hate issues with new stuff =O
HELP
There is no settings to be changed

 

[GhislainG]

RES means reserved.

http://www.hardwarebook.info/ATX_Power_Supply

http://www.hardwarebook.info/ATX_v2.2_Power_Supply

You probably need a new PSU.

 

[thatguy2001]

I built a new computer with a Freezer Pro cooler and all worked fine.
I then wanted to change the cooler with a Xigmatek HDT-S1283 I bought, and when I did and tried to start the computer, it started, a few seconds later it turned off and then continued to do the same thing. Exactly as you are experiencing.

As I had only changed the cooler, It could only have been one thing that was causing the problem.

I put my Freezer Pro cooler back in and my computer started working great again.

For whatever reason, my Xigmatek cooler wasn't making the best contact with the CPU and was causing the PC to restarted after approx 5 seconds after turning it on. I was using the push pin method as I had no retention bracket.

I hope this helps.

 

[Flipparn]

The fan in the PSU is running when ever the powercable is connected too.. that is rly weird? Even when switching to "0" on the big breaker at the back.. fan still keeps goin.. and computer still trying to reboot.... until I pull the cable. Looks I got a faulty one as you said ghis.

Dont think its the cpu fan mate... since it worked with old psu.. tried several times to swap between them. I will double check the fan tho.