clearing the run history

Start the registry editor (regedit.exe)
Move to HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\RunMRU
Select the entry you wish to remove, e.g. h
Press the Del key (or select Edit - Delete) and click Yes to the confirmation
Double click the MRUList value and remove the letter you just deleted. Click OK to save the change
Close the registry editor