Did you see any bubbles ever?
I personally don't like the adage that airlock means nothing, only because I've never ever had an airlock not bubble at least a few days. If I were fermenting a beer and didn't see any activity at all after 5 days (actually for me, after 3 days) then I would open it up, take a look and also take a gravity reading, to see if the yeast were doing anything at all.
Don't get me wrong, I agree that airlock activity only means you have air moving through the airlock, but if you never saw a bubble in it at all, I would say, from my personal experience, it's as likely that your yeast never took off as it is you have a big enough leak to let out that much CO2 to not bubble at all. If you never saw a bubble, imo, that would be worth taking a look at what's going on. If you did see bubbles, disregard everything else I said and just let it ride a few more days.
If you are using a bucket, My first course of action, before just opening the bucket, would be to get a bright flashlight and turn the lights off in the room you are in. Don't open the bucket. Turn the flashlight on and set it light down on the lid. This should give enough light in the bucket that you would see the remnants of the Krousen ring just above the level of the beer. It will be pretty distinctive compared to the beer as it looks messy with usually an uneven line. If nothing has happened, you'll see a distinctly level line. My guess is, you'll see the krausen and can then let it sti for a few more days then take a gravity reading.
If you don't see krausen, then I'd consider a repitch of new yeast.
