In all fairness i believe i am using the green button command. I am using a logitech universal remote and the windows media center database that it uses, the command is titled media. For all intent and purpose it does what the green button does whether it is the exact same i am not sure.
Are you using the Logitech "MC HTPC SE" Device type, with its extended command set?
That is what I am using, and I also use the "Media" command from that set. It appears to function exactly the same as the Green button on the standard MCE remote I have.
The Logitech standard MCE command set, "Media Center PC" has a command called "MediaCenter" which I just tested and confirmed that it also works the same as the Green Button.
Note that when I say Green Button, I mean the large green button with the Windows logo on it, not the smaller button in the Red/Green/Yellow/Blue set.
As to the original question, I have both the server and client start with Windows. If I shut down the client and press the Green Button, or the Media button, MC starts in Theatre View.
If I navigate to the TV Guide and start a program, each press of the Green Button or the Media button toggles between the program playing, the Guide, and the MC Theatre View menu.
If I stop the Media Centre process in the Windows Task Manager then the Green Button does nothing, although the Windows mouse pointer flashes showing that Windows receives the command. I don't even need to stop the Media Centre service to stop the Green Button working.
If I change MC to only start the Media Server with Windows, the Media Centre process and the Media Centre service show as started in the Windows Task Manager, and the Green Button launches Media Centre, starting in Theatre View. It doesn't seem to respect the startup location in Theatre View though, always starting at the top level menu, even though I have it set to "Video".
Just check. Do you have the Option > Theatre View > Disable Windows Media Center ticked? If not WMC could be interfering with the remote commands when MC isn't already running.
Note that I am currently still using MC version 19.0.158.