Computer wont turn on...

[Max123]

Well it does for about 0.5 seconds and then turns off again, then 5 seconds later it trys to power up and it turns off.

I've managed to find out it's when the 8-pin or 4-pin power connecter is plugged in to the motherboard, it just dosn't want to power up. Any ideas?

Motherboard: a-bit IP35-E
Power Supply: Corsair HX 520W

Thanks.

 

[Max123]

It powers up without the 8 or 4 pin connector in, but when I plug them in the cpu fan powers up and then pretty much instantly powers down again and repeats this every 5 seconds(ish)

I've just replaced the motherboard after the previous one was faulty, I had it running fine before hand with the old motherboard for about 2 months.