Is Tor compatible with Windows XP?
Tor Browser no longer supports Windows XP OS. Tor Browser 8+ is based on Mozilla Firefox 60esr which won't run on XP Pro.
Why is Tor not running?
If Tor Browser was working before and is not working now your system may have been hibernating. A reboot of your system will solve the issue. Delete Tor Browser and install it again. If updating, do not just overwrite your previous Tor Browser files; ensure they are fully deleted beforehand.
Does Firefox still work with Windows XP?
Firefox version 52.9. 0esr was the last supported release for Windows XP and Windows Vista. No further security updates will be provided for those systems.