This has been an issue with past models and Toshiba offers software to repair it, hotkey.exe or something.
Also there is software in a Driver Package for the keyboard, but they do not appear to offer this as a download for you machine.
It would appear your options are:
1 - if you have a driver disk try reinstalling keyboard driver.
2 - in the device manager, right click on the keyboard, choose properties and choose update driver. (if you had plugged in an external keyboard at some time, try the rollback driver option if it's enabled)
3 - if you have system restore turned on, go back to a date which it was working.
4 - reinstall OS
5 - If it's new call Toshiba, see if they have a download or over the phone fix for it.
6 - Post in forums on Toshibas website.

Good luck