Is it in a bucket or a carboy? If it's in a bucket, have you looked to see if there is any krausen? Do you know the OG? If so, do a gravity reading. If it's gone down 1 single bit, it's fermenting.
I have an Ale Pale (bucket fermenter) that never shows airlock activity unless it's blowing off some krausen through a blow off tube.. I'm assuming that it has a slight leak some where that the gas escapes through (possibly a bent lid?) Like I said, it never shows any airlock activity unless its blowing off krausen.
Like said above, relax.