I checked and there’s no sign of activity after a few days. What should I do?

It’s possible your yeast was dead. This happens a lot with yeasts packaged with imported “canned kits” or you could have left too much sanitizer in the fermenter. Go ahead and pitch another 10-14 grams of properly rehydrated dry yeast. Be sure to aerate the wort again. A lot of brewers like to keep some dry yeast on hand for such an emergency.