I think the best way is to insert your operating boot cd and reinstall all , or make a bootable disket to enter the console and format it from there.
After this you should allways backup ur software with a free one like http://www.dmailer.com/dmailer-backup.html.
Is a free software that offers you the ability to store the backup online on their servers , and also it has a lot of usefull features in it.