Oh, you already reinstalled? Rats!
For future reference, here is one trick you can use. When the Default value for HKEY_CLASSES_ROOT\exefile\shell\open\command gets changed, thereby preventing any .EXE from opening, you need to run COMMAND.COM

From that, you can then CD into the Windows (or WINNT) folder, and run a COPY command to make a copy of REGEDIT.EXE.

You call the copy REGEDIT.COM.

Then, run REGEDIT.COM, and there you go! You will then have REGEDIT open, and you can fix the Default value for HKEY_CLASSES_ROOT\exefile\shell\open\command so normal .EXE files will open normally. This bypasses the no EXE running problem you had.