@faisalss first try a hardware reset. The hardware reset does not reset the Windows Live ID or remove any of your data. Because you cannot remove the battery to reset the phone, the phone has a special electronic circuit which cuts the phone power when either one of the following hardware reset options is performed.
To perform the hardware reset, press and hold the Volume down and Power keys at the same time for about 10-15 seconds until a short vibration is felt. The phone should restart by itself.
To perform the hardware reset, press and hold the Power key for about 10-15 seconds until a short vibration is felt. The phone should restart by itself.
After that you can try a OS reset. This procedure erases all your data.
Make sure the phone is turned Off.
1. Press and hold the power key
2. Phone vibrates (release the power key)
3. Press and hold the volume down key
4. Exclamation mark is shown on the screen (release the volume down key)
Input the following key combination:
1. Volume up
2. Volume down
4. Volume down
The phone should reset and boot up. If it does not you are having some failed hardware. I'd start with a new battery. Take a look at this teardown Nokia Lumia 1520 Teardown and determine if you want to go that route.