It sounds like a bad bottle. Doesn't happen very often, but 18 hours on a stir plate should be showing activity.
Summer in the mid-west makes for dead yeast. The only times I've had deaders were during hot spells.
Remember one unassailable statistic, as explained by the late, great George Carlin: "Just think of how stupid the average person is, and then realize half of them are even stupider!"
"I would like to die on Mars, just not on impact." Elon Musk