Optiplex gx280 can't get on.

I have recently been given a potholes gx280 small size. 

And I cannot get onto it I have tried pulling the battery from the motherboard and the password jumper turn it on press f2 I reset to factory then change the security  but still can't get in.

When I first turn it on and it comes up with the welcome to windows xp professional screen I ctl-alt-Delete and it comes up with a certain company login notice then I click ok then I have to log in but I don't have a password or account.

Can anybody tell me if the company who's login notice it is would have changed any internals and if so or if not how I can fix my problem so the computer is usable?

Please help me 

Thank you