Tosiba P305D Vista will not start up

My laptop will not start up. I push the start button, it starts for about 3 seconds, then shuts itself down, then starts back up. This just keeps recyclying until I turn it off by holding down the start button. I have tried starting while holding down the F8, F12, and "0". It just acts the same, and keeps recycling, starts itself up, then shuts itself down, and repeats this. I have taken the battery out and tried with just the power cord, and vise versa. Battery only, no cord.
HELP Please.

It's not getting thru the Power On Self Test (POST). Could mean your system board is bad.

You can try pulling the hard drive and optical disk drive out of the machine. See if that shows anything different when you restart. You can also reseat or remove memory modules.