If it seems that your mobile eating your battery, having hanging problem, in this fault you can factory reset your mobile then You will See that your 70% problem has gone, But you can lost your Data so Please create a backup of your mobile before take this action.
But Sometimes problem do not go after factory reset mobile, in this case you have to flash it. not in hanging problems you need to flashing, there are some more reason for flashing your mobile.
If mobile stucked on Logo, automatically Installing apps, deducting your balance. Auto Restarting you need to flash it. Before Start Flashing check your battery for charge, battery should be charge about 70% or more. Low battery may be cause of damages your device.
And More Important is your data as Contact numbers, your some videos with friends or with your family, your photos/images which clicked by you at very rare moments, some favorite songs collections which you collected by hard working all is important. So save your data because as I have already told you that after flashing or factory reset all data will be deleted.
For backup you can copy all contacts at your sim card, for save photos, videos, songs you can use SD Cards, Pen Drive, External Harddisk, Another Mobile whatever you have at this moment of flashing your mobile.
After charge your battery and Save your very very important data, there are some steps of flashing mobile follw this step by step, definately you can do it.
Now We are going to Flash Motorola XT1550 step by step.
Requirement for flashing of Nokia Lumia 520
1. First Download and Install Nokia PC Suit. (Link is given Below).
2. Download Lumia Flashing Tool (Link is Given Below).
3. Download and Extract Nokia Lumia 520 Flashing File.
Steps for Flashing:
1. Put your phone at Flash mode (Press Power and Volume Up key).
2. Connect phone to pc Open Motorola Flash Tool.
3. Open Lumia Flash tool file.
4. Open ‘‘WPID’’
5. Open ‘‘Start’’ Flashing tool will Open.
6. Click on ‘‘Change’’ and select file.
7. Click on ‘‘Flash’’