I understand this should be a fairly simple problem, I just do not have the knowledge to fix it yet.

I have an HP Desktop computer and I am trying to restore it to the factory settings. I have already backed up my important data i dont want to lose, but i can not locate the original OS disk that came with my system. The recovery points that are set for my computer do not go far back enough to take care of the virus and spyware problems I have been having. When I try to delete the viruses, it tells me I am not logged in as the administrator and do not have the rights. I am the only user and I am the administrator on my PC. How do i take care of this problem or reset my machine to the factory settings without the original OS disk?

Comp specs:
HP Pavilion
Product name - KJ379AA-ABA a6400f
CPU - Intel(R) Pentium(R) Dual CPU E2200 @ 2.20GHz
OS - Windows Vista Home Premium SP2

Let's go with the assumption I am an idiot and just starting to learn this stuff in my school... how do I go about doing that? Keep in mind I do not have the OS disks