Is it the camera? Is it the computer? Is it the connection? As it turns out, all of these things need to be in complete harmony or you won't be able to log anything. The first thing that you should check when you're trying to log the footage is that the camera has the correct settings. If you captured in HDV then make sure that you don't have the down-convert settings on. Make sure that the firewire setting is set to HDV and not to DV. Make sure that the camera is in VTR mode and not camera mode.
The computer settings need to match the settings that the camera has. This is actually very simple in Final Cut Pro but can be frustrating if you don't do it right. Under the "File" menu, click on the "Easy Setup" option. In the window that will show up, find the setting that you configured your camera to display. From here you should be all set to log and capture.
If you find that these steps didn't get your camera to be recognized, you'll usually be able to fix the problem with a simple restart of the camera and the computer!