Windows 7? Or Vista if you have an installer disk (you can download a legit installer disk for 7).
Download all the latest drivers from Toshiba even if they are quite old. Backup all of your data and insure that the backup is reliable.
Then just boot from the Windows install disk, select install, and delete all partitions then install to the single unpartitioned space. Reinstall drivers, reinstall all of your programs, and then copy all of your data back.