Dampen a cotton swab with some anhydrous isopropyl alcohol and carefully wipe the heads. These are the metal pieces that read the cassette, situated at the bottom of the cassette dock. Gently dry the heads with a new, clean swab.
Press "Play" on your tape recorder deck so that the capstan--the metal spindle to the right of the cassette heads--spins. Gently wipe the capstan with a cotton swab that has a little anhydrous isopropyl alcohol on it.
Clean the black rubber roller--the pinch roller--that guides the tape by slowly turning the roller using an anhydrous isopropyl alcohol-dampened swab. Wipe dry with a clean cotton swab after. Clean the fixed metal and plastic guide posts using the same method. Wipe all parts with a dry, clean swab to make sure all moisture is removed.
Find a location not too close to your audio equipment to plug in and switch on the demagnetizer. Demagnetizers can be purchased for under $10 in electronics stores or online.
Move the tip of the demagnetizer slowly towards the tape heads. Move the demagnetizer back and forth across the tape heads, but don't allow it to touch the tape heads.
Slowly pull the demagnetizer away from the tape heads. Switch off and unplug the demagnetizer.
Check the electrical cord on the back of your cassette deck; if your tape recorder doesn't work at all it may have a loose connection. Take your cassette recorder to a professional electronic repairs shop if this is the case; rewiring can be dangerous.
Press "Rewind" or "Fast Forward" on your cassette recorder; if these functions don't work then there could be a problem with the belt or the idler. Take your tape recorder to a repair shop if this is the case.
Play a cassette in your player. If it stops unexpectedly, or won't stop playing at the end of the tape, their could be a problem with the pinch roller. Unscrew the front panel using a screwdriver and remove the deck. Lift the roller assembly of the shaft and replace with a new pinch roller, available in stereo repair stores.