I just got the notification for the Android 5 update, so before doing the update I wanted to backup all my photos and phone data to my PC just in case I lose some data (unlikely but I like to be safe).
I plugged my phone into my PC (Windows 8.1) and found that it no-longer works AHHHHHHHHHH.
What I found from searching around is that a Windows update has stopped the phone from being recognized properly. I did find lots of articles about removing drivers and all sorts of other stuff but this is a lot of work and most did not work.
To resolve this all I had to do was install the Media Feature Pack for Windows 8.1
After install my phone connected straight away.
I Hope this helps you with any issues you may have.