Its possible a problem on the Hard drive but 1st try the following:
1. turn OFF the notebook.
2. disconnect the AC adapter (if its plug-in)
3. remove the battery of the notebook
4. press and hold down the power button for 10 sec. without the battery and AC adapter connected to the computer.
5. then reconnect everything to the notebook (battery and AC adapter)
6. power ON the computer.
7. if you still have the same problem. call toshiba tech support if your notebook is still in warranty to replace the hard drive.