|First of all, you may be able to put your laptop to the factory condition, to the exact day you had bought your laptop. You must read the documentation that came with your laptop or the on-line documentation in Toshiba web support site.|
If this is not possible and you have the Windows 7 DVD disk, then you should boot to Windows 7 disk and do the formatting and Windons installation from there.
Perhaps, you can also try to recover your installation by repairing Windows (repair installation ). Repairing can be done after booting to Windows disk.
To be able to boot to Windows 7 DVD disk, you may need to change the boot order to DVD drive in BIOS.
For Windows 7 clean ( from scratch ) installation, please see this tutorial.
Hope the above helps.