How are you judging the lack of fermentation activity? I ask because airlocks on buckets are notoriously silent due to the lids not sealing tightly and CO2 escaping via that path instead of the airlock. Do you see kreuzen or remnants of one on the sides of the bucket? The only way to know for sure is to take a gravity reading. If the gravity is still at your OG then you need to pitch new yeast. Lastly what temperature are you fermenting at? Cooler temps, which is where most lager yeasts like to be, take longer to get going. But, I would expect you would be seeing some evidence of fermentation after 3 days.