Computer won't complete a System restore to any restore point?

I have windows XP and ever since I re installed it my computer does not complete system restores. I try any date and every time it tells me the restoration wasn’t incomplete and no changes have been made to my computer. Any idea why it does this? Has done this since I completely wiped my PC so I don’t think it’s a virus. (also being as I’ve done like 40 virus checks since that time) What could this be?