Why is my iPhone 6s screen only displaying a few seconds aft restart?

I just replaced the screen and the battery to no avail. I was having issues getting the charging port to work originally(few days before), then it did this. After hard reset the screen comes up then disappears a few moments later, no indicator as to why. I noticed once it went off when the raise to activate turned on so I turned that off, still has the same issue. Also weird I don’t see a boot logo. My phone wasn’t turning on at all until I noticed the connector next to the battery came loose. I only see two water sensor stickers and neither are colored nor do I have a reason to suspect water damage. Thanks for any ideas, theories, or assistance