At first I thought having CM11, 4.4 kitkat was the problem. So I flashed a stock-based rom and kernel. Still no success.
My Xperia V is not being detected in Windows 8.1. It's only detected when using MTP or MSC, not Flash mode of fastboot mode. Before you start throwing "You must disable Driver signature enforcement" at me, flash and fastboot works for my Xperia Z1. I'm trying to relock my Xperia V's bootloader so I could give it to my uncle. Look at the attachment to see what message I got from Windows when connecting.