Not sure what you mean by "command" Command prompt?
But either there or in the start, it should open. Look in Windows and see if the file exists. (Windows\Regedit.exe) If it does, see if it runs from there.
hi I had this problem, do this it may work:
go to C:windows
then search (Regedit.exe) press right click (click" run as administrator")
now you will see the regedit
then go to this address :HKEY_CLASSES_ROOT
go : exefile\shell\open\command ok now open the Default and
change the Value data to "%1"%*
then go to: runas\command and do the last way( change to "%1"%*)
Now it's finished, and you done