Is their a possible leak in the fermenter lid? Are you visually seeing no activity in the wort, itself or are you drawing this conclusion from an airlock that is not bubbling? If airlock is not bubbling, it could be many explanations, one of which would be yeast related.
Relax and give it time. You pitched enough yeast for a five gallon batch at those temps. Look inside, if you must, but it is likely fermenting away happily.