In iTunes my iPad would not connect to my Windows 7 PC with Avast Firewall turned on.
Worked with Avast Firewall turned off.
Tried lots of things, in the end the solution was simpel:
Even if there is nothing else wrong with Avast, find Installed Programs, find Avast, rightclick and choose “repair”.
(Probably the same will do for android connection problems in other programms)