There could be a number of reasons. A loose connection, power adapter fault etc.
Try removing the battery from the laptop and see what happens when the mains power supply are then turned back on.
You could also have a look at this link for Toshiba information http://www.ehow.com/about5912125toshiba-laptop-battery-problems.html
Doing a simple internet search, there appears to be a number of Toshiba laptop charging problems mentioned, with some possible solutions.
Failing that, have you tried Toshiba support and customer care?.