Use the set of recovery discs which you (should have) made when you first bought your laptop.
If you didn't bother making any, you can order a set from Toshiba via their website:
Europe: https

/backupmedia.toshiba.eu/
USA:
https
/support.toshiba.com/repair
(scroll down to "Get Recovery Media", enter your laptop's serial number, then click "Go").