Erica, this is in fact a fairly spectacularly wrong place for this - it needed to be a new thread under trimmers.
I am not familiar with your machine and I haven't followed your explanation well, but you said in Shout Box that you have a fuel starvation problem. One fairly common source of this problem is the air vent into the fuel tank not working. You can check whether this is your problem easily by leaving the fuel tank cap loose and trying the trimmer outdoors with no load, keeping the fuel tank cap pointing upward. Please be very careful, because if you tilt the trimmer fuel will spill out near a running, spark-ignition engine.
I'd appreciate it if Bruce or Deejay would move these posts to a more suitable place - I don't have a clue how to do it.