Using the system restore feature bring the system registry back to that point not restore any files lost by overwriting or deletion. For that a data recovery tool would probably be the only method of retrieval to consider there.
Active Undelete has a demo for file recovery seen at
http://www.active-undelete.com/
As far as seeing Windows itself restored when no restore points are available and continual problems persist that would be the repair install method outlined at
http://www.michaelstevenstech.com/XPrepairinstall.htm