Exactly the same problem here, so any hints on how to check it woudd be appreciated. I suspect I somehow damaged the phone. I had the USB connection working properly for several months and then it suddenly stopped. It still charges but the PC no longer detects any kind of a data connection, there are no USB device messages etc. When connected, the phone gives me a choice of mass storage mode and other options as before and it all seems OK from this end.
I have tried reinstalling drivers, using different cables and PCs and even performed a factory re-set on the phone to no effect. A phone repair shop inspected the USB connector and saw no physical damage. Suggested a "board" damage. The phone was rooted and I had a lot of stuff on it when it stopped working. I am not an expert on android and rooting, so perhaps this condition is still somehow reversible?
How can confirm I have a hardware (board) problem?