A couple of things to try;
Restore the registry from a recent backup.
or
Explorer|Tools|Folder Options|View and uncheck the box for "Hide extensions
for known file types" then copy regedit.exe as regedit.com Then create these
*.reg files and import;
-------------------------------------------
Windows Registry Editor Version 5.00
[HKEY_CLASSES_ROOT\.exe]
@="exefile"
"Content Type"="application/x-msdownload"
[HKEY_CLASSES_ROOT\.exe\PersistentHandler]
@="{098f2470-bae0-11cd-b579-08002b30bfeb}"
------------------------------------------------
------------------------------------------------
Windows Registry Editor Version 5.00
[HKEY_CLASSES_ROOT\exefile]
@="Application"
"EditFlags"=hex:38,07,00,00
[HKEY_CLASSES_ROOT\exefile\DefaultIcon]
@="%1"
[HKEY_CLASSES_ROOT\exefile\shell]
[HKEY_CLASSES_ROOT\exefile\shell\open]
"EditFlags"=hex:00,00,00,00
[HKEY_CLASSES_ROOT\exefile\shell\open\command]
@="\"%1\" %*"
[HKEY_CLASSES_ROOT\exefile\shell\runas]
"Extended"=""
[HKEY_CLASSES_ROOT\exefile\shell\runas\command]
@="\"%1\" %*"
[HKEY_CLASSES_ROOT\exefile\shell\View Dependencies]
[HKEY_CLASSES_ROOT\exefile\shell\View Dependencies\command]
@="G:\\PROGRA~1\\MICROS~3\\Common\\Tools\\DEPENDS.EXE /dde"
[HKEY_CLASSES_ROOT\exefile\shell\View Dependencies\ddeexec]
@="[open(\"%1\")]"
[HKEY_CLASSES_ROOT\exefile\shellex]
[HKEY_CLASSES_ROOT\exefile\shellex\ContextMenuHandlers]
[HKEY_CLASSES_ROOT\exefile\shellex\DropHandler]
@="{86C86720-42A0-1069-A2E8-08002B30309D}"
[HKEY_CLASSES_ROOT\exefile\shellex\PropertySheetHandlers]
[HKEY_CLASSES_ROOT\exefile\shellex\PropertySheetHandlers\PifProps]
@="{86F19A00-42A0-1069-A2E9-08002B30309D}"