Fermentation question

I have noticed a lag in the fermentation (bubbles in airlock) in my current batch of English Brown Ale I brewed Sunday evening. I pitched dry yeast and added it to the wort within 2 degrees of the wort temp. at 74 degrees. Outside temperatures have been cold recently and I was storing in my basement where the wort was registering 64 degrees on the bucket thermometer. Is the low temperature stalling the fermentation? Since its nearing three days (7:30pm tonight) could there be a yeast problem? Any advice?

Thanks

Which dry yeast did you use?