Windows XP has been deprecated for a while now, so viruses are the least of your concerns.
If your father doesn't want you to reinstall, then grab an free anti virus solution (Like Avast) to at least clean it up a bit.
If you're still running windows XP without any kind of anti virus you should be asking yourself if you want that PC connected to the internet.
You're probably in hundreds of botnets, mining coins and sending spam to people.