iPhone 7 don’t work!

My wife's phone had the same problem on her iPhone 7 plus rather than your iPhone 7, but the fix should be the same.

In my case, replacing the Proximity Sensor Light Motion Flex Cable + Front Facing Camera (bought on eBay) resolved the issue. I tried all of the software solutions I could find on the internet with no luck until I ran across a post that talked about fixing the problem by unplugging the front camera. I did that and it worked and ultimately found that replacing that cable finally fixed it for good.

I would definitely advise trying out the software solutions first, including forcing a hard reset and doing a restore (if possible); just do a general search on "iPhone 7 boot loop" and you'll find quite an assortment of suggestions that don't involve opening up the phone.

For your phone, my best guess would be to buy the iPhone 7 Front Camera and Sensor Cable, available here from the iFixit store. As a bonus, it also comes with all the tools needed to do the repair. You can also opt to buy just the part without the tool kit and display adhesive.

As I mentioned, you can test this out first before buying the part by opening up the phone and unplugging the front camera. If that allows it to boot, then go ahead and buy the replacement cable and that will almost certainly fix the problem.

Complete instructions on this repair are available in the iPhone 7 Front Camera and Sensor Cable Replacement guide.