From the chatter that I've read on this forum my first guess would be they've shut down and moved everything to digital (SARA). In the menu of your scanner there is an ANALYZE feature that will allow you to call up a system and select a site. If you're getting a signal the graph will show it, of course having a signal present doesn't mean they are broadcasting on it.
If you are monitoring SARA and still not receiving anything then verify your getting a signal. Then look for the obvious culprits; SERVICE TYPE not turned on, squelch to high (3)