Legacy 1394 Drivers for Windows 7
If you ARE connecting the camera to the PC/laptop AND you are running Win7 you are going to need to get busy with the Legacy Drivers for that 1394 port. It is dead easy, even I did it. You will need to activate the LEGACY driver for the 1394 port. For some reason known only to Microsoft, MS doesn't set-up the 1394 in a way you and I need, even on install Win7 might well have been able to "see" it. However, we need the port to be compliant with the appropriate driver, and here we need the port active for video capture flow. It's not the video, it is the port being made available.
So, for Win7:
1/- RIGHT Click Computer > Select: Manage
2/- In Computer Management > Select: Device Manager
3/- In Device Manager > Select: IEEE 1394 Bus Host Controllers
4/- In IEEE 1394 Bus Host Controllers > Select:1394 OHCI Compliant Host Controller (Legacy)
If you can't locate it immediately, do some sniffing about in that menu. It will be "hiding" in a multiple dropdown selection menu, it was for me.This, as suggested in the naming, are the drivers for "Host Controller".
If this is the issue, I had this and once I had switched to this Legacy option I have Vegas porting out to my CRT ProMonitor; my ancient Panasonic DV Deck able and ready to port in miniDV tapes and your experience should be the same with HDV tape. It is solely the drivers for the, I suppose "chips" in the Host Controller still requiring a driver from way back. If this is your issue, then this is nothing to do with the content of the stream: SD, HDV or your camera and its software.
Why it worked for you once? You would fortunate, as was I. But after that one time the port was dead to Vegas, or any other 1394 device worked-through that port. Doing the Legacy thing, and getting success, I subsequently I ripped out my ACEDVio card from my previous PC and installed it in my new Win7 machine and these Legacy Drivers having been working a storm since. I can switch from my 27" LCD monitor to my JVC ProMonitor from within Vegas 12 without issues.