If you have a data backup then one option would be to force a factory reset on the phone and the just restore everything from the backup. Automatic backups need to be manually turned on so if you are unsure or don't know whether you've turned it on or not then I do not suggest you do a factory reset since it will wipe all data on your device. Your backups should be accessible from Samsung Cloud or your Google Account.

At first this sounded like a possible power supply issue but since there was no relay click after you disconnected the mainboard I would suggest you check for any damages on your mainboard and your T-board. I believe the issue might be revealed there. Maybe the dent caused minor but critical damage?