If the yeast does not have a foamy/frothy layer on top it has not been proofed properly. In this case, you will need to repeat this step until you have a properly proofed yeast. It is essential that the water is up to temp to ensure successful proofing of the yeast. It should be warmed to 105-110 degrees. It's best to use a kitchen thermometer to gauge the temperature. If you don't have one, simply test it with your finger. To touch, it should feel like a nice warm bath. Also, make sure your yeast has not expired. Sometimes the yeast may just need an additional five minutes to proof.