Take the plug out and with it firmly mounted in the rubber boot of the CDI hold it against the cylinder head and with ignition on slowly rotate the prop past the magnet on the prop shaft. See if it sparks when passing. Make sure your CDI batteries are charged etc. If you have the original Melody CDI module with the SPE26 them the chances are that it may be cactus. Mine lasted a few flights before failing, the next one lasted a few more and eventually I purchased a RCXL module that has worked well ever since.