Does this happen while charging or with the FP just laying there?
If it’s while charging and the LED blinks red, then your battery is deep discharged.
- Make sure you use a high quality USB data cable, a compatible charger and the battery sits well in the frame (fill eventual gaps with folded paper).
- Then try the battery reset from the #batteryguide.
- for reference this would be the issue discussed here.
If it bootloops without being plugged in take off the cover.
Slim covers are known to sometimes cause reboots because of stuck buttons. Switching power and camera button usually solves this. (that would be this topic)
If it’s neither of those two issues check out the first post here.