How do you know that there are 8 profiles in the computer if you cannot log into it?
If the PC came with the Windows XP installation CD and the Certificate of Authenticity with the Product Key, you will just need to re-install the operating system. After you boot from the CD (you need to go to BIOS by pressing I think the Del key a couple of times after you power on the PC), you will get the chance to delete the existing partition from the hard drive which means that you start from scratch.
If your PC came with the Dell recovery CD(s) and you boot from it, it wipes the hard drive clean before re-installing the operating system with the drivers and the applications provided by Dell.