Read the instruction manual that comes packaged with the laptop computer... it will tell you how to do a restore. It may also have a link in the Start Menu that can be clicked on to start the restore process. It will be impossible to do unless you have restore disks or install files on a hidden partition of the hard drive. If you have neither, then you won't be able to do a restore.... in which case, Toshiba Tech Support should be able to help you. I don't know the exact steps used on a Toshiba but with my HP laptop, I can start the restore process by pressing the F10 button during bootup. Most laptop makers have different keystroke to start the restore process. Nearly every pc comes with a recovery drive but every one has a different key to press upon boot. If this doesn't work, either call Toshiba or use Google for Toshiba recovery partition.
I'm having to consult my memory for Toshiba laptops but I believe this will be the steps:
"To access the Toshiba recovery partition, power off the laptop. Hold down the 0 (zero) key and turn the laptop on. Keep holding down the zero key until the TOSHIBA logo appears, where you should start tapping the zero key repeatedly. Stop if the unit beeps or when the TOSHIBA logo disappears. The screen should flash ** HDD RECOVERY MODE ** for a split second, then load the Toshiba recovery program right from the hard drive.
Note that this erases all data, and reloads all factory default software. Be sure to back up all your important personal data beforehand!"