Go to settings > Security > Mark "Unknown sources"
Settings > Developer options > Mark USB debugging
Settings > Xperia > connectivity > USB connection mode > select MSC mode
PC Companion installed on your PC.
1) Connect your phone to PC and wait for the adb drivers to be installed. If these drivers don't get installed, phone would not be detected by Eroot.
Make sure nothing else is running on your PC in the background.
2) Download rooting toolkit. and run it. If any downloading starts, cancel it by clicking the green button. Don't let the eroot download anything.
It should now detect your phone and show an option to "-root". Just click on it, wait till it finishes
3)Rooting done, If by chance it fails for the first time, give it another go. it won't harm your phone in any way.