I am totally new at testing apps on devices, especially the Sony Xperia. I am testing apps using the Android emulator, but I have now a Sony Xperia. First I have connected
I had same problem with my Xperia Z3+ (android 5.02) with Android studio 1.3. I installed new drivers and XPeria Companion but it didn't help. However after I enabled hotspot via USB it started to work. Don't know if all of these was needed of if it was only the last one. Anyway I did 1. Settings->More...->Internetsharing hotspot->USB-sharing to on. 2. In the pop-up accept USB debugging.
This answer is more general to not finding your device. But if you have dead ADB processes running, you might have to kill them (and start a new one) in order to pick your device.
Download the correct driver for your phone, make sure your phone has enabled USB debugging and then connect it to proceed with the install.
Download drivers from: http://developer.sonymobile.com/downloads/drivers/