Share your experience!
The mobile internet on my Xperia T is getting often disconnected. I thought switching off and switching on the phone might help. So I switched off the phone. And now its not switching on at all in spite of many efforts. I have not done any system update etc. recently. I cannot imagine what could be the reason of this sudden issue.
Try to connect to PC companion and verify if is correctly recognised. Then try a firmware repair
If the same i believe that is a motherboard issue and your device needs a repair