An airlock is a vent, nothing more. Vigorous airlock activity means that there is fermentation, but lack of it does not mean that anything is wrong - CO2 may be leaking around the airlock, or if you are using a bucket (which tend to have notoriously leaky seals), from around the seal.
The ONLY way to be sure that fermentation is going on is to use a hydrometer and take a gravity reading. If you don't have one, spend the $8 investment to improve your beer.
My advice? Leave the beer alone for at least a week (preferable two) before you even bother taking a reading. You'll see that many of the bets here tend to do 3-4 week primaries; patience can be a good thing.
No matter what, don't start worrying about the beer when you are measuring it in days in the fermenter.
- blogging about making my own beer and raising a lot of kids.
Check out the priming sugar calculator
and the beer calorie calculator
Fermenting: American brown ale
Bottled: big Irish red ale, Thundersmoke brown ale (Yorkshire brown), Belgian golden strong ale, imperial nut brown ale