If you are describing the problem I think, I have experienced the same (also opening Excel files) when opening a file by double clicking within Windows Explorer. I believe it to be a conflict between Windows Explorer and the application (SE or Excel). If you deselect the file in Explorer i.e. select another file or close Explorer, then all the commands in the application (SE or Excel), become available.
Hotkey applications come in different forms. AMD/ATI video drivers have a hotkey application I try to disable on any systems where they apply. Some keyboards, mice, and 3d input devices have their own hotkey apps. Laptops usually have some sort of hotkey handler for funciton key management and touchpad fuctions. The list goes on.
@uk_daveHMMMMMM. I think you might be on to something here. Let me run some experiments. I'll see if this might be the culprit.