Ok I just replaced my screen and had the endless reboot problem. Fix Repair shop where they restore the phone. Took them several try's. they kept getting error 9 but eventually got it. 35 bucks. I asked them what I might have done wrong during the screen replacement. They said it looked like the power had come back during the process and corrupted the software. They suggested disconnecting the battery next time.
Philip I have same problem after changing my screen. Initially, phone would not power up after screen change, but unplugging the battery got it going again. Now it reboots just as you explained. One thing to add. I let it reboot until the battery died. When I pushed to power button it showed me a stable battery mode message indicating I needed to plug in phone. As soon as I plugged it in it went back into continuous boot mode. Headed to repair store today.