Hmmm, well, I'm fresh out of ideas. What i would do however, is this:
Back up all your data, then install a fresh copy of XP. Sometimes system files can go corrupt over time, it's happened to me a few times, so I wouldn't rule that out. I would however back up all your data regardless if you want to reinstall or not, because if it gets worse soon, you might lose important files, so i would back up your data ASAP just to be safe.