check you are using the line out or pb out sockets on the tape deck.
also check you have plugged it into the line in socket on the pc, not mic.
I use nero wave editor (part of nero burning rom) to transfer stuff from records and tape.
be sure to keep your originals though if they're unique recordings- its easy to delete files by accident or the hard drive could crash. i also have cd-rs burned 7 years ago which have deteriorated beyond use, yet the cassettes still play fine! sometimes the old stuff is the best......