Toshiba Satellite A200 Boot Issue

Hi all, strange problem here- I have a Toshiba Satellite A200 running 32bit Vista that does not boot up fully. When connected to the a/c power and I hit the power button the "on" light flashes on for the briefest moment then nothing. Six to seven seconds later it repeats this and continues doing this until I unplug the a/c. That occurs with the battery both in and out of the unit. If I try a start up on the battery with the a/c disconnected the unit powers up with the initial toshiba logo screen but during the boot process it just shuts itself down.

Things I have tried so far- Removing ram + hdd then bleeding of residual power = no change.
Swapping both ram and a/c adapter for ones that I have with another A200 that work perfectly = no change.
Tried booting up in "safe" mode to disable processors but it loads windows then immediately re-starts before I can access anything. If I start up and go to f12 boot menu I can hold that screen all day long and navigate the menu list without it shutting down. Tried re-setting to factory defaults in that menu but no change.
Removed internal extraction fan to check for blockage causing overheating and replaced heat sink paste = no change.
Another thing it does is, if I start it on battery and then plug the a/c adapter in, it shuts down immediately. Both a/c adapters are working fine. Also the battery recharges fully via the a/c adapter no problems.

Any idea's would be welcome as this has got me stuffed