Where do you have it plugged in? The rear DATA connector is preferred.
Does it switch to transmit or just sit there in receive?
Are you sure the computer audio is turned on? I normally keep the audio on my PC muted, so I have had that happen several times.
Do you see the waterfall display on the screen?
You should be going through the rear DATA connector, and the FT-817 should be in the DIGI PSK31-U mode. All of this should be in the manual. I don't have a Signallink USB sound card, but I did make an interface for a friends FT-817. He had HRD and Digipan running on a Netbook running XP. The interface was simple and consisted mostly of wire. A USB to Serial interface was used for PTT keying. A one transistor circuit was built into the serial port connector hood. It worked great. I put it in the 1 watt mode and used 20M PSK-31. I received an answer from across the country in a couple of minutes.
You may want to check the audio output connections. I used standard 3 wire 1/8" phono plugs for connecting to the audio in/out. However, some PC now come with the audio in and out in the same connector. These systems use a 4 wire plug.
I have things running on several computers from Windows 3.1 to Windows 7 64 bit. But I never had to deal with Vista.
73, Martin, K7MEM
Ash Fork, AZ
In my area, it seems that every pickup truck or SUV comes with one or more dogs. It's so common that I can only assume that the dog(s) must come with the vehicle. So logic tells me that, if you want to keep the truck for a long time, go for the multi-dog option. Otherwise, if the dog dies, you have to buy a new truck. I have five dogs (4 dogs as of 4/4/2013, RIP Katie), so I'm set for a few years.