As others have already said, the next step to troubleshooting should be to try a different radio. That will rule out (or in) the power, feed-line, and antenna. I'd do that before spending any more time troubleshooting the radio.
If the radio is suspect, here are some questions I'd ask myself:
If not the antenna, feed-line, or power, perhaps the receiver circuitry is malfunctioning. Does the S-meter register any received signals?
Perhaps the internal speaker is blown, shorted, or otherwise malfunctioning. Have you tried an external speaker?
Rotate the volume and squelch knobs back and forth several times. Sometimes dust or corrosion can cause the potentiometers to malfunction and working them a bit will free the contaminant. Also check for "dead-spots", in that there could be one or more spots where the volume cuts out completely, even though it's not turned down at all.
Did the radio get wet? Was it operated outside of acceptable operating temperature? If you remove the cover, are there any fuses visible? Are any blown?
Good luck...
