As LeoRex said, the boot loop is most likely a hardware defect, and a factory reset won't help anything.
There is one trick you can try if you need to back up the phone. Stick it in the freezer, battery and all, for 15-20 min. With it still in the freezer, boot it up. This should give you enough time to do what you need before it can heat up enough to cause the boot loop. If you need to plug it into a computer and can't bring that to the freezer, you can maybe try sandwiching the phone between a couple ice packs. At this point, I'd also suggest encrypting the phone before doing a factory reset to make sure all your data is wiped when you file the warranty claim.
The freezer trick is specific to the G4 due to the common defect with a bad connection on the main board. It won't work with boot loops caused by other problems.