SMART Board MX75 V3 Troubleshooting for Teachers | SMART MX75 Review 

In a case like this, you can try. However most likely the lock screen will persist on start. Because the unit runs on base android utilizing the factory reset button may be necessary. This will completely erase everything though.

Turning off the switch will work, but it is not safe to do so, as it can brick your board. I've said this on another comment: Press and hold the power button until "Slide to save energy appears" Then slide and afterwards wait until the board's light turns red, turn it back on again. You should be greeted by the SMART logo followed by a loading icon. If you have an OPS module plugged in, your display may instantly boot to there instead of IQ. To fix this, press the HOME button on your display

I no longer work with these boards, but this might be of help. community.smarttech.com/s/article/How-to-manually-restore-interactive-displays-when-stuck-on-the-Updating-screen?language=en_US

If the home button lights up it's not an issue. If the light turns green and the board turns from black to grey, it is also not an issue. If the board light turns green, and nothing happens you can contact smart support now

Are you getting a specific playback error that is being listed on the video frame?

A work around to test would be in the browser click the 3 dots on the upper right side. Then look for an option that says "Request Mobile Site"

hdmi cable needs replacing

Check if your OPS module is seated correctly. You may also need to replace it, otherwise, you can contact SMART support. If the home button lights up, that just means it's trying to boot

Press and hold the power button until "Slide to save energy appears" Then wait until the board's light turns red, turn it back on again. You should be greeted by the SMART logo followed by a loading icon. If you have an OPS module plugged in, your display may instantly boot to there instead of IQ. To fix this, press the HOME button on your display

Note: You have to slide to the right to shutdown

On the first boot, your board can take up to an hour to boot

I no longer work with these boards, but usually there is a factory reset button that can be accessed by a paperclip on the android module.