Mculloch Hedge Trimmer won't start?

Got problems starting my Mculloch Hedge Trimmer (I believe the model is Tivoli 60 or 65), it died during operation. and only briefly re-started thereafter. Cleaned air filter and spark plug, all engine parts are moving, re- greased gear box, changed fuel, but with same from container, gues I need to try with some fresh fuel mixture. Metered a voltage from spark plug cap when pulling starter cord. Should I replace the spark plug can these fail suddenly ?

Gary