If the engine runs fine but the cutting head on the trimmer will not turn please see the following checks:
First, check to make sure that the engine housing is slid all the way down on the shaft. The engine housing should sit flush against the black indicator line on the shaft.
If the engine housing is not the problem, then there could be a problem with the flexible cable. On units that utilize a flexible cable, please check your operator's manual in the maintenance section under "Lubrication" to see how to access the flexible cable. Please click here to locate your operator's manual online. Once you remove the flexible cable, inspect the cable for any damage.