It could be a cable, It could be the port on the cam, they have been known to blow if hot swapped, same with the port on the computer, I would find another cable to test with and if that doesn’t work, try another computer, and or try to connect two camcorders together via firewire and see if they will xfer data between them, process of eliminajtion, when connecting to computers don’t do it when both are on, connect with both off and then bring up.