It sounds like your carburetor is likely clogged. The carburetor can become clogged by dirt or other debris. If fuel is left sitting in an unused trimmer for more than a couple of months the fuel will begin to breakdown and go bad. As the fuel breaks down it will start to become gel like as well as begin to coat the internal parts of the carburetor with a varnish. The gel and varnish will plug the carburetor so that fuel can no longer flow through it. To get your trimmer running again you will need to either rebuild or replace the carburetor. When you replace the carburetor it is always a good idea to also replace the air and fuel filters. This helps ensure that more debris won't clog the new carburetor.
There is not a carb kit available for your trimmer so the carburetor will need to be replaced. The carburetor is part #753-04229, the air filter is part #791-180350B, and the fuel filter is part #791-682039. All of these parts are available from http://ereplacementparts.com.
I hope this helps with your repair!