Locate the problem with your reel to reel. Turn on your tape recorder and try to pinpoint the faulty component(s) before doing anything else.
Unplug your reel-to-reel, and take it to an area with a flat work surface and enough space in which to work comfortably.
Dampen a cotton swab with tape head cleaning solution, available online or in your local audio store, and gently wipe the reel heads. Leave the reel heads to dry for a while. Load in some more tape once the heads have dried, and try making a recording as a test.
Using a screwdriver remove the screws in the covering plates and gently lift the plates off. Check for any loose parts, and tighten any you come across; loose parts can often cause problems for a tape recorder.
Remove and replace any parts that don't seem to be working properly. Purchase replacement parts from specialized stores or websites. Replace the covering plates, and screw the screws back in.