What to do about yeast that doesn't work?
You can proof your yeast to see if its still alive:

Heat approx. ½ cup (100ml) of water to about 115°F (45°C). Add a tablespoon (10g) or so of sugar, stir. Water should still be above 105°F (40°C). Add a teaspoon of yeast, stir. Within 5 minutes or so, the mixture should be thoroughly foamy.

If its not thoroughly foamy, yeast is bad (dead), dispose of it.

(Note: Metric conversions above are rounded, just like the imperial units. Don't use these conversions for baking, but proofing yeast doesn't need anything exact.)