PC boots then restarts

Hello,
Problem - Turning the power on will result in a restart within the first 3 seconds, then it will load up to the bios splash screen before it restarts and repeats the process of Short time restart then longer time restart.
At the bios splash screen i am unable to access the bios in any fashion.
In terms of bios settings none have been changed ever since getting the system(april 2011).

Some things i tried were using single ram stick with both of them.

Unplugged mouse/keyboard/optical drives.

Using a different power cord from psu to hdd

Things i have not done include taking out sound/gpu/cpu.

Are you able to attempt to boot without a hdd installed, would this have adverse effects if i tried to turn it on without one. What are the core components that must be in to start up a PC.

Specs
mobo - gigabyte p67a ud3r - b3
CPU - Intel i5 2500
GPU - gigabyte 460 SOC
RAM - Gskill ripjaw 2x4gb
HDD - wd cavier black 1tb.

If there is any other information i can give let me know
 
Please can you keep the discussion of this problem to one thread, as it will just confuse those trying to help you.
 
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