Use the links in my above posting to get to the power board and replace it..
The common problems in Toshiba laptops:
No power at all: Bad power chip, open circuit, short circuit, or loose connection.
Symptoms:Nothing showing up when you press the power button
Also since you have it open it would be a good idea to clean the heatsink in that model
Toshiba Satellite M55
You can easily clean the heatsink and the fan if you remove the keyboard from the lapop (Steps 1,6,7,8,9,11). If the laptop is warm in the area of the hard drive, it is possible that hard drive will fail soon.
http://www.irisvista.com/tech/laptops/Tosh...therboard_1.htm