The method with the zero button is really helpful and the fact you can not use it is quite unfortunate. Your next option is to use recovery discs. In this case you need an existent recovery partition and some DVDs. You should run the Toshiba Recovery Disc Creator from the Start Menu Programs. If your laptop is not working properly and creating those DVDs is not an option, you should contact the reseller and ask for assistance, especially if the product is under warranty.