Screen gone black.

[Maximmus]

This is the second time my mobile's screen going black. The first time the mobile automatically restarted, but in the second time I had to look for the restart button and restart it my self. Why is this happening, and how can I prevent it from happening one more time. (I don't want to do a software repair...)

[Phy]

You should repair with pc Companion as it could be an app acting up or something else

Sony PC Companion.
http://support.sonymobile.com/us/tools/pc-companion/

[Phy]

You could also boot on safe mode and check it


How to boot on safe mode.
http://talk.sonymobile.com/t5/FAQ/How-to-boot-your-phone-into-safe-mode/m-p/348008#U348008

[Maximmus]

My phone's screen doesn't turn off automatically. What shoul I do.

[yankeeee]

try to force it to shut down 

and open it again by using power button and volume up 

if it is not working repair your software through pc companion and keep it not connected until it asks you to connect.

Kindly note that it is preferred to back up all your data before repairing your phone because some of the information in your phone might be lost during the repair process.

Kindly be sure that your phone has enough memory as the update takes some of the phone memory.

Kindly be sure that your phone battery is more than 90% while you are repairing your phone.