I take it that you have frequencies programmed into the scanner, so this is the solution to your problem.
On the keyboard of your radio scanner you will find a button marked L/O or L/Out, when your scanner is in scanning mode, press the Mon or Hold button, this will stop it from scanning.
Now select the channel of your programmed frequencies, starting with Channel 1. To do this press Hold followed by 1, if this channel shows a L/O icon on the LCD screen, press the L/O button and the L/O icon should go out. continue through each channel, until you undo the L/O from each channel by following the steps I have described above, once you have removed the L/O icon from all the channels that were locked out you can then press the Scan button and you'll be listening to the frequencies that you programmed into your scanner.
Note: If you have not programmed any frequencies into your radio scanner, then you will not be able to hear anything, as nothing programmed to hear and L/O is the default setting on all channels, until each one is programmed with the frequencies of your choice.
How to Program a frequency?
Press Prog button, select channel to store frequency, E.G:Ch:1 168.5000
Remember to always press the (.) decimal button in the correct place, else you will get ERR message on the LCD, now press Enter button, you now have the first frequency stored in you radio scanner on Channel 1, now press the Delay button, so that it doesn't start scanning for 2-3 seconds after a transmission is received.
Continue with the above setup one channel at a time until you have programmed your radio scanner to your liking.
I hope I have helped you in finding the solution to your query.