Can't run programs on Vista. .exe not recognised?

After what looks like a virus attack, I can no longer run programs on my laptop. When I click on a program (e.g. Internet Exporer) it brings up a window with a list of programs that I might like to open it with. I think the association of the .exe extension with the ability to just run the program has been lost in the registry.

If I run the program from the DOS command prompt, then it works just fine. Do you know how I can restore the registry setting back to the correct setting? (I can run regedt32.exe from the command line)

Thanks