Go into recovery mode in Sony Live With Walkman
Do you use any custom kernel or do you have stock factory default?
IF you don't have stock then there is no recovery.
If you have a custom kernel, you should press the VOL DOWN button when you see the KERNEL logo. That's because custom kernels have CWM recovery integrated, because Xperia 2011 phones don't have a the recovery partition.

For solution to your problem, you should use SEUS, that's the only way to fix a bootloop with stock kernel.
You can download it from here: http://www.sonymobile.com/global-en/tools/update-service/
The software is self-explanatory and will guide you how to enter into flash mode.
Here's a tutorial on how to use SEUS: https://www.youtube.com/watch?v=H_OCgB6ASqQ