No Administrator password

I bought a Optiplex 755 computer, cheap. When I fired it up, it has a win 7 pro system. I was going to put in my XP, but would like to stay with win 7, as long as it's installed. I quickly found out that I couldn't do much of anything because I don't have the Administrator user name or password. The User Account Control asks for this info whenever I try to change something. I can't even delete the win 7 to put in my XP. I took the battery out and pulled the password jumper, but it still wants the info for the UAC when I try to load something. From what I looked at online, I figure I'm stuck with this setup. Any suggestions?

I just saw this from a previous posting.............. Oh well....

Posting methods to bypass security such as activation or encryption or even a simple password is considered illegal and as such this is as far as we can take it.

If you can create an install Media, (likely to be a DVD on this age of PC ), for your Windows XP and have your original Retail Key, (OEM keys that came come with pre-installed copies of XP, Windows 7 Etc are one off use and cannot be used on other than the system they were sold with), you should be able to install a fresh copy of XP (wiping the current Win7 Install in the process).

The reason we have our rule about not helping with password issues is that we cannot confirm your actual ownership of the system, this is unfortunate but does not in anyway suggest we think you have done anything wrong. If you have a local technician it should be possible for them to unlock your system very quickly and cheaply as you should be able to prove your ownership to them quite easily so the issues we have as a remote entity are not valid