PC Companion and Win 8.1
I found it very frustrating to update my Xperia T to the recent 4.3 release. PC Companion will still backup your phone nicely. I could see that there was an update, but PCC would tell me that it needed to be used in a previous version of Windows like Win 7 (?). Now this is incredibly stupid, but as we all know, there is always another way. I reinstalled and also chose other USB ports; no go. So I searched for answers and saw references to Compatibility mode - no matter what mode I chose however it made no difference. References to a recent MS fix had no relevence - it was already installed and not making any difference here. So I installed Java and also installed SEUS. I was able to get that going but it only showed recent various Sony products but not my T - argh! So after a few hours of of frustration I was no further ahead. Then I saw somewhere a suggestion for adjusting Compatibility Mode for SEUS - bingo that was the ticket. So the short version: Using Win 8.1 PC Companion is not going to allow the Update function to work, but SEUS will work, after switching it's compatibility mode to Win 7. Hope this helps.
moto a854 with cm7.2, tf300 16gb with CM 11 , Xperia T, rooted Stock 4.3