Android Sony Xperia SP keeps restarting

I updated my phone to 12.1.A.0.266 a few weeks ago through wifi when Sony released it officially. And now my phone keeps restarting.It doesn't even reach the home screen. Factory reset(under the back panel) and any hard or soft reset doesn't work.

It all started after I updated the phone to the new firmware. The new UI was slow and laggy. Sometimes when I used to pick up the phone speaker used to be switched on.

From a few days, the volume on the screen just showed a horizontal bar and not the actual volume UI.
3-4 days ago Chrome crashed and 2 days ago Google search and Google now crashed. I installed Amazon kindle app for Android last night but that too crashed in the morning.

And from afternoon, the phone itself crashed.

How do I get my phone back to life?
 
Back
Top