No service messed up settings to where it shows unkown bootloader

Safe Mode for ZTE Prestige 2:

1. To enable the Safe mode, with the device Turned On, press and hold the Power key until the Power menu appears.
2. Tap and hold Power off.
3. Tap OK.
4. The device will restart in Safe mode, press and hold to unlock the screen.
5. To disable the Safe mode, press and hold the Power key until the phone turns off.
6. The device will reboot into normal mode.

If that fails, you can try a Dial method.

This method requires you to open the dialer first after which the below steps is to be followed.

1. Enter this code *#*#4636#*#* in the dialer
2. Enter Service mode
3. Click on the top option, – Device information or Phone information
4. Next, tap on Run Ping test
5. Radio option will be visible at the bottom of this screen
6. Check if it is off or on and then press the button next to it to turn on radio.
7. You will be prompted to reboot the device.
8. Click reboot and your phone will start rebooting. Once completed, check if the problem is resolved.

Now, if that fails too. It could be the IMEI Number being nulled/corrupted.

1. Turn your device on and go to the dialer to enter the code (*#06#) which shows up the IMEI number of the device. In case it shows ‘Null’, the IMEI number is corrupted and should be configured to resolve the ‘Samsung Galaxy and Android No Service issue’.
2. Dial (*#197328640#) or (*#*#197328640#*#*) from the handset dialer which display command mode. # Users are required to select the option ‘Common’.
3. Next, select the option 1 that is Field Test Mode (FTM). It should be made off if it was ‘ON’. This process will change and restore the IMEI number but ensure to press the menu key button before you leave the # Command screen, as this is a vital step to make the changes effective.
4. Choose key input and select option 2 which will turn off FTM.
5. Now, remove the battery and SIM card from the device, wait for 2 minutes after which re-insert the battery but not the SIM card.
6. Turn on the device and type (*#197328640#) again from the phone dial.
7. Next, go to Debug screen> phone control> Nas control> RRC and finally on RRC revision to resolve the # Null IMEI or not registered on network issue.
8. Now tap on the released your phone is, which is normally option 5.
9. Turn off the phone again and insert the SIM to find out if the no service issue is resolved.

Sources: My own knowledge and from here: https://www.quora.com/I-have-no-service-...