azn_fishy, you may not have a good seal. I thought I was having problems at first until I realized that my glue job wasn't very airtight. The other possibility is that you used hot water instead of warm water. Hot water will kill yeast.
I ran out of white sugar but I have a gallon jug of corn syrup that's been under the sink for months now. I put 3/4c in a 2L bottle for my 20G, and 1/3c in a 733mL bottle for my 10G. Let's see how they do for the next little while.
I've also seen alternate recipes, such as using sugar suspended in gelatin and allowed to set, and then topping off with yeast and water. Apparantly, the yeast eat their way down, and apparantly, if you add food colouring to the gelatin, it'll actually serve as a time indicator as to how much life the bottle has left in it. It sounded complex, but that's going to be the next step.