First - is there water in the pump basket. The pump basket is the small canister (about the size of a coffee can) with the clear plastic top on it. Very slowly turn it to release the lock and then while keeping pressure on the lid, open the lid a little. This will let any air in there come out. When water starts to come out, push down on the lid and clamp it back on.
If that seems a little much for you, you can put a winterizing plug in your skimmer (or turn off the suction side valve if you have one) then open the pump basket, fill it to the top with a bucket, close it back up and then remove the plug (or open the valve)
The pump is not self priming - meaning if there is air in it, it will never start pumping untill you add an initial "charge" of water. When you pump began to suck air, it lost it's prime.
Now, if you re-prime the pump and you still have problems, then we have to look at some other things (such as maybe you burned out your pump by letting it run dry)
You should also be cleaning out that pump basket every so often as well. When you do that you do need to install the winterizing plug or turn the valve (if you have one) off. There is a strainer basket in that chamber that is intendend to catch anything the skimmer basket misses before it gets into your sand.
-dave