Something isn`t working properly here

I have a bread machine. I go through times where I use it often, and then times where I don`t use it for months.

A couple of weeks ago, I went to make bread and it didn`t rise properly.

I had two containers of yeast in the cupboard - one that I suspected was too old to use, and another that I thought was OK. When the bread didn`t rise properly, I assumed I had grabbed to wrong one.

Today I did an experiment to determine which container of yeast was still usable. The results: both are too old. I need to buy more yeast.