Android Wife's phone bricked

Recently the display on my wife's Redmi 7A used to go off as soon as she makes or picks up a call, and stayed off. I couldn't find anything in the settings that could cause this. So, following advice on the internet, I pressed the power and volume- buttons together. The phone turned off but would not turn on again. It's effectively dead.

Any suggestions on what do next?

Thanks for the reply. I already did that but it still would not turn on. I'll try it again when I have time.