Toshiba m300 charging trouble, stops charging when...

Question

It seems to charge fine as long as the computer is turned off. As soon as I start the computer, the charge lights go off and the computer does not recognize that it is plugged in. This means that I can only use the computer for a couple of hours, then I have to turn it off and re-charge the battery for a copuple of hours before continuing to use it.
Help!