Could be any number of things.......
First, the most basic question. Do you have the owners manual? If you don't you should be able to get it from RS on-line. Read the manual cover-to-cover, especially the troubleshooting section. If nothing there helps, try the following tips:
I don't mean to insult your intelligence, but sometimes the obvious things go right by us. When you turn your radio on do you turn the volume up to a normal listening level? Next, does your scanner have a Mute button? If it does that might be your solution.
Now that we've got the basics out of the way:
Since it is a programmable scanner check to see that the radio is still programmed with the frequencies you entered. Programmable scanners have a memory that will retain the programmed frequencies if the radio is unplugged for any length of time. If that circuit is not working you will lose your programming if you unplug the radio. You might even lose the programming just by turning the radio off. Depending on the model you may also have to reprogram the various operating modes for the radio to receive properly. Again, refer back to your owners manual if necessary.
If the frequencies are still in the radio as you entered them, then check the squelch. Again, I hope I'm not insulting your intelligence with this step: A properly set squelch is when you turn the squelch back to the point that you hear white noise/static. You then turn the squelch back up to just past the point where the noise stops. If you have the frequencies in right and the squelch set right, next check your antenna. If your antenna is properly attached you should be receiving signals. An easy way to test your radio is to tune in the National Weather Service. NWS transmissions are on a continuous loop. If your radio has the WX button, simply push that button. If it doesn't have the weather frequencies pre-programmed you can enter 162.550 MHz. This is the frequency that is broadcast from Riverhead, Long Island, NY. I assume you're from Long Island based on your posting name and listening interests. If the radio receives NWS it should receive while in the scan mode.
If these basics don't restore your radio's ability to receive, and nothing else you might read here improves things, I would take your radio to an electronic repair specialist.
Joe P, KC2PJL
Charter Member of the Red Knights International Motorcycle Club, NJ Chapter 15
Amateur radio....the only REAL radio left in the world.
Emergency Services Dispatcher