What kind of beer recipe did you use? All-grain, extract or one of those Cooper's kits? It's possible the yeast you used was bad to start with (especially if it was from a Cooper's kit, who knows how it's been treated along the way...)- However, the curdle you saw was most likely kräusen- a sign of active fermentation.
When you stirred, did you sanitize the spoon? If not, you're risking infection. 2 hours is not enough time to see any real change in your beer. The yeast need time to readjust to their environment and continue fermenting. Leave it alone for at least 2 weeks and take a hydrometer reading before bottling anything. If you get 2 readings that are the same 2 days apart, you're good to bottle.
You'll read this a lot here and it's good advice to heed - airlocks are not a good indicater of fermentation. They only serve to expel CO2 and prevent nasties from getting into your beer.