This little trick can help you come across frustrating period, like the phone keeps rebooting without any reason….
Step 1 Unplug the power cable from the phone and then plug it back in.
The phone begins its power up cycle.
Step 2 While the phone is powering up, and before the Speaker button
flashes on and off,
press and hold #.
Continue to hold # until each line button flashes on and off in sequence
Step 3 Release # and press 3491672850*#.
You can press a key twice in a row, but if you press the keys out of
sequence, the factory reset will not take place.
After you press these keys, the line buttons on the phone flash red and
the phone goes through the factory reset process.
Do not power down the phone until it completes the factory reset process
and the main screen appears.