When I first got my MiniDV camera, it worked fine. I unplugged it and later tried to use it, but kept getting the "no camera connected" message. Turns out my Firewire port just died. I was able to get it working again by resetting the nvram.
The procedure I used:
1) Shutdown
2) Unplug all but mouse & keyboard & monitor
3) Startup
4) Hold Apple-Option-O-F
5) At prompt type: reset-nvram (hit return) - It will say OK
6) At prompt type: reset-all - It will say OK
Shutdown
Attach all cables and restart
Everything worked fine after that.
This page might help in case that does nothing.