Having a build issue

[sainix]

Having an issue on my new build i just put together.

first 2 times i turned it on it posted, i have not installed os yet.

now i turn it on light goes on the mobo light goes on cpu fan spins, then the comp turns off fan stops spinning then a few seconds later turns on agian and just keeps repeating

why would this happen all of a sudden?

nzxt phantom
ud3p gigabyte mobo
2500k i5

atm i have a old 7300le gpu in it

Corsair 650tx psu

stock heatsink
ripjaw x 4g cas 6 1600 ram

 

[masterasia]

could be anything.

Ram (try booting with only one stick, try different slots)
GPU (try booting without the GPU in)
MB (bad motherboard?)