I haven't had that happen but my Montage did previously shut off on its own after a timeout period (if there were no active edits). This is the default configuration in order to meet some country's power conservation laws. It can be disabled and after I disabled it the shutdown no longer occurs.

Here's a video showing the settings:
https://www.youtube.com/watch?v=OuBqIan5NWA

This doesn't have anything necessarily with the "it won't turn back on" problem. However, disabling the turning off may help mask this issue.

I think probably what happened is the auto shutoff relay (or solenoid - or whatever it is) got stuck and traveling between the gig and home shook this loose. You may have been able to get this worked out had you lifted the Montage 7 up and let it fall (an inch or two - nothing drastic) back on the stand.

EDIT: BTW - I'm not sure how grounding would impact things either. It's possible that grounding (like lift, or no ground due to wiring at the venue) may impact how this feature works. In which case perhaps it wasn't a mechanical issue as mentioned before but more of an electrical one. This is fairly wild speculation since I haven't reviewed the schematics (which I have) to see if this would have any impact in reality.

Thanks for you reply Jason. But do you think that the keyboard would auto switch off while I'm playing it? This is what happened to me. I was caught by surprise. I think that it was an electrical issue but I would like to know the cause to prevent it from happening again although it is only the first time after one year that this occurred.

It shouldn't - but I would still check that setting and switch it off.

My problem was I would come back from a break between sets and the keyboard was shut off.

I think sometimes I saw it shut off during a gig but I was probably playing a different instrument at the time.

After turning that feature off - you may, certainly, still have an issue. I'd just let that roll and then if you still have an issue consider a service event.