No application/utility will launch

PC running Windows XP Home
System will boot to the user profile (only one user) but when they click on an icon/glyph the application associated with that icon/glyph will not launch and the system is nonresponsive for several seconds.

I have booted into safe mode and run Adaware, Spybot, and Norton AV and then ran the disk defrag utility. However, the anomoly still persists.

NOTE: Prior to all that I attempted to restore the OS from a previous checkpoint but the restore would either not execute or made no difference.

The PC came from a shop that is no longer in business and does not have OS media. Don’t want to do a destructive rebuild …