|It's extremely unlikely properly un-installing McAfee has anything to do with your problem - you probably have something else that is causing your problem. |
If the guy was the original owner, the computer probably came with a Dell XP Re-installation CD. If you can still contact him, ask him if he still has it.
In most cases that CD can't be used with anything other than the model it came with anyway, at least, not for installing Windows from scratch or for running a Repair installation of Windows procedure.