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.