You can try and activate with the activation wizard (the keys icon) in the system tray. After the EOL the activation was still working, but that may have changed. If it doesn't then you don't have any other option to activate. If you are connecting to the internet you are putting yourself at risk of being compromised since XP is EOL and there are plenty of now unpatched vulnerabilities. If you're not willing to upgrade, you may want to consider installing a Linux distro on the computer since it will be up-to-date and should work just fine on older hardware. Linux Mint is a good beginner distro and can even be themed to look a lot like Windows.