So nobody mentioned the whole "didn't rehydrate" as a culprit - just a couple that want to not believe it is. We know better than this now, it's not the 90's. I have had outstanding results with dry yeasts when rehydrating. I've also started using Go-Ferm for wines but that may be overkill for beer.
Rehydrate, pitch, watch blowoff start very soon, that's been my experience. After looking through a microscope at some yeast that had not properly rehydrated I was a believer. This article is a good read - you can figure out what applies to beer vs wine:
MoreWines Guideline to Hydrating Active Dry Wine Yeast & A Recommended Nutrient Regimen for Fermentation
As I said I don't think Go-Ferm is needed, but it does not hurt and makes for some remarkably "violent" fermentation.