I have an older toshiba laptop and i want to reset it to factory defaults because it used to be my sisters and now its mine. help?

Try this
Hard Disk Drive Recovery using the recovery partition
You have the options of recovering your system using the Hard
Drive Recovery partition to the factory-set default, or recovering
just your C: drive and leaving other partitions (for example, a D:
drive) intact, or changing the size of your C: drive and then
recovering it.
To recover your hard disk drive using the utilities stored on your
computer's HDD:
1 Make sure the computer is turned off.
2 Press and hold the 0 (zero) key on your keyboard while
powering on the computer. When the computer powers on, the
Toshiba Recovery Wizard screen displays.
3 Select one of the options, and then click Next. The options are:
? Recovery of Factory Default Software
? Erase the hard disk

1 On the Toshiba Recovery Wizard screen, select Recovery of
Factory Default Software, and then click Next.
The Recovery of Factory Default Software screen appears.
(Sample Image) Recovery of Factory Default Software screen
2 Select Recover to out-of-box-state, and then click Next.
A confirmation message displays reminding you that all data
will be lost during the recovery process. Be sure to save your
work to external media before proceeding.
3 Click Next to begin the recovery.
Once complete, a message displays that the HDD has been
recovered.
4 Press any key on the keyboard to restart the computer.
To recover only your C: drive:
1 On the Toshiba Recovery Wizard Screen, select Recovery of
Factory Default Software, and then click Next.
2 Select Recover without changing the hard drive partitions.
A confirmation message appears, reminding you that all
information on the C: drive will be lost during the recovery
process. Be sure you have saved your work to external media
before proceeding.
3 Click Next to begin the restoration.
Once complete, a message displays that the HDD has been
recovered.
4 Press any key on your keyboard to restart the computer.

If you do not have the original restore dvd it can be purchased from the Toshiba website with the serial number from the bottom of the computer for 13-14 bucks shipping, the OS is already licensed to that computer so your not charged for it. Just did the same myself and 14 dollars is not bad to invest in a laptop.

If you have the original DVD you can just put it in the drive and select boot from that device when prompted.