Computer Booting Problems

I'm new to building, and have just recently finished putting it together. However, when booted up, the computer only stays on for a few seconds, beeps one short (indicating success) and the powers off. From then on, it continues a cycle of powering off and on at erratic intervals, however it does not beep at all during this phase.

I did follow this guide before posting this - http://www.tomshardware.com/forum/ [...] o-problems , however if you think it is one of these solutions don't be hesitant to say it. There's no harm in trying it again, rite?

I'm thinking it is a PSU problem - I turned the supply switch on and off again repeatedly to turn off the computer off due to a cpu fan problem.

I replaced the CMOS battery, and tried booting it with only one stick of RAM as well. Also, the bootscreen shows when powered up, but I can't get into any of the menus before it powers down.

My build:

Zalman Z11 Plus
Gigabyte Z68MA-D2H-B3
i5 2500k
Gigabyte GTX 560 Ti OC
Thermaltake TR2 600w
G.SKILL Ripjaws X F3-12800CL9D-8GBXL