While there are a number of specialised hardware products on the market that will enable you to play and record audio cassettes to your personal computer, users with a modicum of technical ability can easily devise a solution that will get the job done. If your cassette player has "line out" (also known as "audio out") connectors, you can jury-rig a connection to your PC that will allow you to play your audio cassette through your computer speakers. Here's how:
Verify that your cassette player has "Line Out" or "Audio Out" RCA connectors. These are female plugs, usually colour coded red and white, about 1/4" in diameter. (If your player lacks "Line Out" connectors, you may still be able to connect to your PC--see "Tips" below.)
At an electronics store, purchase a cable with a male stereo mini-jack plug on one side and a pair of RCA plugs on the other. This is a standard cable used to connect audio components, sometimes called a stereo patch cable or a Y-cable. Colour match the red and white RCA connectors to the red and white line-out plugs on your cassette player. Plug the male mini-jack into the "Line In" input of your computer.
Turn the volume to low on the cassette player and play a cassette. On your PC, open the windows mixer, then Options>Properties and select "Line-In". Slowly turn up the volume on your cassette player until you hear the cassette playing over your PC speakers.
If you are having trouble getting sound from your speakers, first verify that the "mute" button isn't checked on your PC. Next use Windows Sound Recorder to attempt to record and play sounds coming from your cassette. If the sound records, the problem lies in the Windows Mixer settings. Otherwise, systematically check your cassette for output, the cable for connectivity and the working of the PC line-in jack.
After you're able to play a cassette through your computer speakers, you might consider using the open-source (free) program Audacity to record your cassettes to your PC. After you install Audacity, open the program and click on Edit>Preferences>Audio I/O and change the Line-In options until you get sound input. Press Record and Stop to make the recording, then choose File>Save Project As>Export As>MP3 to save.
If your cassette player lacks RCA output jacks, try this: find an audio cable with a male stereo minijack on either end and connect the player's headphone jack directly to the PC's "line in" plug. Sound quality may not be as good as a RCA-to-minijack.
If your computer lacks a "line-in" connection, add an internal sound card available at most electronics store. An inexpensive one will work as well as an expensive model, because the quality of the sound will only be limited by the quality of the cassette recording.