The beer has been in the primary fermenter for 12 weeks and you are not sure if it fermented? Couple of things you need to check/answer.
1) Was the beer in a bucket or glass carboy? If it's in a bucket, the lid could have been loose which is why you didn't see any activity through the airlock.
2) Have you taken any hydrometer readings to determine if fermentation occurred? Even if you didn't have the initial reading, an estimate should have been provided with the kit, and you can check the reading now to see if anything happened.