Nokia Lumia 638 hard reset1. Turn the power Off.
2. Press and hold the Volume down and connect the charger or the USB cable with PC, for about 8 seconds, you will see an exclamation mark (!) on the screen. Note: If you do not press any of the following keys, then the phone wp8 will starts boot normally.
Then press the keys in this exact order:
1. Volume up
2. Volume down
4. Volume down
Phone will restart, be patient.
Use Nokia Lumia recovery tool
resetting your Nokia Lumia 638 from menu
Reset your phone. This restores the factory settings, and erases all your personal content, including apps you've purchased and downloaded. On the start screen, swipe left, and tap Settings > about > reset your phone.
All data will be lost!
Factory reset Nokia Lumia 638 from the menu
On the start screen Scroll down to the bottom of the screen. Tap arrow.
- On the Start screen, tap .
- Tap Settings > about phone.
- Tap reset your phone, and then tap yes.
Nokia Lumia 638 soft reset
If your phone freezes try to reboot it.
Press and hold the power key for over 8 seconds. The phone will reboot.
Update your phone software.