Vista Fix
Yes, the same problem appears to happen under Vista as well as prior versions of Windows. The method described here should work but you have to do a bit more work as there is presently no .REG file download FILExt has created. When sufficient numbers of people have tested this there will be a more formal writeup with a download.
If the Vista EXE association is damaged the location in the registry most likely changed is in this key...
[HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\FileExts\.exe]
The "OpenWithList" and "UserChoice" subkeys probably have some program listed as opening the .EXE file extension. These need to be cleared and, when cleared, the system will go back to the default and the EXE extension should then work again.
You can do this by creating a .REG file with these lines in it...
Windows Registry Editor Version 5.00
[HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\FileExts\.exe]
[HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\FileExts\.exe\OpenWithList]
[HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\FileExts\.exe\OpenWithProgids]
"exefile"=hex(0):
Use cut/paste to copy these five lines to an editor like Notepad and then save the file with a .REG file extension. Copy the file to the misbehaving Vista machine and double click on it (or right click and select Merge). You will likely have to say OK to a number of different things (the user access control and the registry editor for certain) but afterward (and a restart to be certain) the system EXE association should come back.
User Travis provided this link to REG file fixes for a number of extensions for Vista (only)...
* Registry fixes for Vista file extensions (including the EXE fix)
If you find a more elegant way to do this please let FILExt know so it can be added here. And, remember...
Warning!
Editing the System Registry can have seriously affect your system. Make no changes to the System Registry without having a complete backup of important files and only after setting a System Restore Point.
Shameless ripped form
http://filext.com/faq/broken_exe_association.php
Out of interest how did this come about?