xp errors for kernel32 dll and access violation errors

The system is abruptly shutting down, hanging, or nonresponsive. Windows and Applications are nonresponsive to commands. Help & Support, as well as most other Help Files no longer open. Error messages indicate a file isn’t there and others become “Invisible.” I have AVG 7.5 Internet Security and run Counter Spy with Threatfire. Also am running periodic scans with other virus and spyware programs. I use Registry Mechanic and perform regular maintenance. Any help greatly appreciated.
Lost in Cyber Space, gardenercook