Follow these steps when troubleshooting tablet screen freezes or stops responding.
Important: Before you start this procedure, make sure the AC adapter is connected to the tablet and load is connected to an electrical outlet.
NOTE: After each step in diagnosing the problem, check the state of the tablet to see if the problem is resolved.
Press and hold the power button for at least thirty seconds. 
NOTE: If the tablet is turned off, press the button again to turn on the tablet. If the tablet is turned on, you can use it normally. If it does not light, continue to the next step.
If the tablet is still frozen or unresponsive, you should follow these steps to start a process of External Data Reset (Resetting external data) forced.
Important: Unfortunately, due to the process of restoring the tablet back to the condition it was when it was initially acquired, all the tablet data and settings will be deleted.
- With the tablet completely off, press and hold the button Volume Up (+) (Volume up (+) and, without releasing the button, press and hold the button Power (ON) for several seconds.
- Once the logo appears Sony , release the Power .
- Continue holding the button Volume Up (+) until the display Android system recovery (Android System Recovery) .Once this screen appears, release the button Volume Up (+) .
Important: Sometimes the mere fact of initiating the screen Android system recovery is sufficient to return the tablet to the standard condition and may not need to perform the procedure for External Data Reset . For this reason we recommend that you quickly press the button Power (ON) to cancel the reset and to initiate the tablet again. If the tablet is turned on, and you can use it normally, no need to take further action. If the tablet is still not functioning normally, repeat the above steps 1 through 3, and then proceed to the next step.
- The screen Android system recovery , use the button Volume Down (-) (Decrease the volume (-) to highlight Reset to factory settings (Factory Reset) .
- Quickly press the button Power .
- The display reset to factory settings (Factory Reset) Confirm reset (Confirm reset) , use the button Volume Down (-)to highlight Yes - delete all user data (Yes - delete all user data) .
- Quickly press the button Power .
The above steps should solve your problem. If you have completed all the steps and the problem persists, you probably need to send the unit to service.