There are two areas to look at here.
First the FireWire driver - have you updated it? When I got my new PC last year the FireWire would not work, my Dealer spent all morning sorting the problem. In the end he changed the card (new PCs rarely come with FireWire built in) and found a driver that worked.
Second the FireWire cable - has it worked before on another PC with the HV30? I have the HV20 and had problems with the first cable I bought, the reason was that the plug into the HV20 was just too short to make good contact. I replaced the cable with another make and it works fine now. The fact that the Handycam works OK suggests that the cable might be the problem.
Remember to switch everything off before plugging in the HV30. Many a HV has had its guts blown by plugging in a live FireWire cable!!
I now have a Panasonic HC-V700 with SD card (as well as the HV20) and it is a much easier system.