Continuous Restarts

[Smithers475]

Hello, I'm having an issue with my Galaxy S21 Ultra and hoping someone might be able to point me in the right direction. I had the screen replaced last year and having the battery lifted out to do so damaged the battery. The battery expanded and started putting pressure on the flex cables inside. Before I realized that battery was expanded the flex cables started coming loose when the phone was knocked/dropped etc. I replaced the battery and the antenna flex cable as one side of the pins got bent. Even after this, all 3 flex cables have still been coming loose, including the antenna flex cable. I've been frequently having to open the phone back up and reconnect them (would I need to replace the mainboard seeing as the replaced flex cable is still coming loose too?). Now suddenly the phone has stopped working, it won't even boot up anymore. While unplugged nothing will happen but while I have the phone plugged in it will turn on but keep restarting on the Samsung splash screen and just keeps looping until I unplug it. With what has happened I'm guessing this is being caused by a hardware issue but I'm not too sure how to go about pinpointing the issue. Any help would be greatly appreciated.