If you turn off system restore you will lose all your previous restore points.
If you are willing to lose them and have the full xp cd then reinstall System Restore.
Go start then run type in
and click ok
Go down to the file "sr" and right click and choose install.... if it asks then point it towards the i386 folder on the XP cd.
Remember you will lose all previous restore points and will need to make one there and then.