Computer Build Problem....Only Powers on for a second then powers off

I'm currently trying to build a low end computer for a family member. After assembly, I am having a problem where the computer will power up for a split second, then power off. It continues to do it every 5 seconds or so until I unplug the power supply.

I've tried without the ram as well as any other connections, save the CPU. I've tried resetting the BIOS as well. Still having the same problem.

Here are the specs:

PS - Cooler Master eXtreme Power Plus 500W
Mobo - Gigabyte GA-H67MA-D2H-B3 Socket 1155 Intel H67
CPU - Intel Core i3-2100 Dual-Core Socket LGA1155
Memory - G.SKILL Ripjaws X Series DDR3 1600MHz 4 GB

I don't have a dedicated video card for it, its only being used for web-browsing and email.

Has anyone seen this problem before or have any ideas what could be causing this? I don't have an extra power supply or CPU lying around so I can't really start swapping parts.

Any ideas would be helpful and greatly appreciated