Exe files are unrecognized

I have a box running Win XP Svc2 and all of the application extensions are not associated with an application. I can not start any exe files. I can not run any applications including regedit. I can run regedit from the command prompt but I can not edit it or import the registry fixes. When importing reg files I get an error saying that some keys are open by the system or other processes.
Any thoughts?