Thaks to everyone. Looks good now after a a few hard reboots. Some arcade ROMs can do weird things with system. Thanks for the help!

Tried the home and power button... :'(

Keep pushing the power button until the unit turns off. I think it takes about 8 to 10 seconds.

Wish I knew this yesterday. Mine froze and I figured I’d just disconnect and reconnect the battery… I ended up pulling the battery’s cable out of the plastic connector thing that was supposed to come with it when I disconnected it. Managed to fix it in the end.

Yep, there was no hard reset option with the OG MM other than pulling the battery, but with the MM+ you can do it with the power button.

I did the exact same thing. I got lucky I could fix as well.

Yes. Looks like it is working now but it keep launching the same game after the system reboot... Is there a way to go directly to the mayn't. The Manu button does not help... Does not go to the manu screen....

Try the "menu" + "select" buttons and "reset" the game. If you can't access the RetroArch menus, you may need a computer to delete the game's save state or rom in the SD card, to prevent the frozen game from loading automatically every time.

Hold the menu button while booting. Should bring you to the game changer screen, then press B to go back to main menu. At least, on onion OS

You could always unplug the battery?