First, connect another source to the preamp's "tuner" input and see whether you hear anything. It could be a problem with the preamp input selector. A CD player or even a turntable should produce sound, but be sure to check the input you are trying for the tuner.
If that works, run that same cable from the preamp to the tuner. If you do get sound, the original cable from the tuner to the preamp could be bad. Cables and connecters seldom fail both channels simultaneously.
If you don't get anything from the fixed outputs, try the variable outputs. If the variable outputs work but not the fixed output, at least the tuner isn't dead.
Is the tuner silent on both AM and FM? Does the signal strength meter move as you move across the dial? Does the stereo indicator light up?
Exercise the front panel switches by moving them through all their settings several times, then reset them to the correct settings and try again. If a switch sits in the same position for years, it can oxidize.
Double-check your antenna connections for AM and FM.
Good luck!