This is the most common problem of all, never trust the airlock as this often means little as to weather your brew is fermenting properly. Usually the brewer assumes the brew is not fermenting so “Out she goes” when often it is perfectly fine! Fermenters do not always seal well and if not sealed, the air lock doesn’t bubble.
First, assess the situation properly by taking a hydrometer reading or by looking for visual signs of fermentation (a ring of foam around the water line, or condensation in the lid is a good sign). If the brew is still fermenting, seal it as well as you can and allow it to finish. If it is already finished, bottle immediately. Don’t throw it out without sampling a small amount out of the tap, as it’s quite possibly OK!