Active yeast

There's an important lesson here: One really should not activate yeast in milk unless the milk has been scalded and cooled. There's something in milk that inhibits yeast activity if not scalded first. If you don't care to scale and cool the milk, use water and reduce the other liquid in the recipe accordingly.
That said, consider this. For many years, recipes for bread made using milk always called for scalding the milk. A lot of people thought that was for health reasons, due to possible contaminants in milk. As milk processing advanced, people started ignoring the "scald the milk" instructions. You get a much better loaf if the milk is scalded. Plus, heating the milk makes it sweeter tasting, which improves the flavor of the bread. ;o)

If your yeast isn't foaming after 5 to 10 minutes, you can try adding a pinch of sugar to give the yeast something to eat and see if that activates it. If it still doesn't foam, start with a new packet. It is possible that the yeast has died if it isn't foaming and if you continue with the bread dough it won't rise with dead yest, so best to start fresh.