The first three things that come to mind are;
1. You have an anti-virus running that is interfering… boot to safe mode and run the restore from there.
2. There is not enough free space on the drive for the restore process… delete (or move) stuff.
3. The restore point file is corrupt… this is un-likely but there is no fix for it.
The results of ended support can only be guessed, no one really knows. But the fact is, sooner or later your XP will stop to work. You need to update to at least Windows 7, also taking consideration with others on the Internet.