It didn't work for me but this did (I got this answer from another website)...
All you need to do is a simulated battery pull
A simulated battery pull will simply tell the phone to reboot, to turn itself off and then back on. This simple tool is amazing for a frozen or locked up Sony Xperia, or if your phone is showing a white/blue/black screen, if it’s having navigation problems, or for any reason you can’t seem to power the phone off yourself all you need to do is the simulated battery pull.
To do a simulated battery pull on a Sony Xperia you basically follow the same steps as you would when doing a simulated battery pull on the Motorola Atrix HD, all you have to do is hold the Volume Down button and then the Power key and hold these two buttons down simultaneously for about 15-20 seconds. After holding them down for about 20 seconds if the phone didn’t power cycle then release the keys and try and turn the phone on like you normally would by briefly pressing the power button.