POCO MIU I Fix Without Data Loss
1st method Long press the POWER BUTTON until the phone Reboots
2nd method long press VOLUME UP+POWER Button until you the RECOVERY MODE then Reboot to SYSTEM
3rd method via Fastboot mode( this is very useful if your Buttons are not working properly)
4th method insert Sim Card then try to call the phone number of the sim card,
if all fails and still not working properly try the 5th method
5th method Long Press VOLUME UP=POWER Button the tap WIPE DATA then WIPE ALL DATA then CONFIRM. this will Format your phone and it will erase al\ll the Data on your Internal storage.
NOTE: make sure to backup all your DATA regularly you can save all your data on the Cloud Storage such as Mi Cloud,Google Drive or cloud Storage