Lately my toshiba satellite A205-S5853 is acting weird. When I power it up on battery, it powers on, the hd starts up, the fan starts up but everything shuts down in like a second. I thought it was maybe that the battery didnt have enough power, so I plugged in the AC cord, same thing, so then I figured maybe the battery was causing a short, so I took out the battery and unplugged it from the AC and pressed the power button to dissipate any static. Then I plugged in the AC and left the battery out. Same thing happened.

What is going on, can it be fixed without having to buy a new mobo  I'm not as knowledgeable as many of the experts on this board but until one of them chimes in with a SOLUTION I'll try to help.
 Does your machine have multiple memory modules installed? If so you can try removing the module from the lower slot 'B'. Then try STARTING your machine. If this "shuts down in like a second" issue still exist then REMOVE the memory module from the top slot 'A' and replace it with the module you previously REMOVED from the bottom slot 'B'. Now try starting the machine with the 1 module installed in the top slot 'A' only.
 If the issue still exist try this:
 I had an issue similar to yours on my Toshiba Satellite L355-S7915. I cured that issue via BIOS update. Hopefully this will cure your issue also.
Now if I can remember how I did it: 
Try pressing F8 KEY repeatedly immediately after power on. If this works then you should be able to select the start-up option 'Safe Mode with Networking'. Then download and install the BIOS update from Toshiba for your Satellite A205-S5853..
 Hopefully this will solve your issue. If not then I'll need to let one of our more experienced members help you.
Good luck! 
Mike