Are you able to operate the derailleur manually (by hand) with the cable disconnected? The other question is, when you are trying to shift is the shifter moving but not the derailleur?

If it was working before you attempted to adjust it, you may have messed something up. You may have both limit screws too tight not allowing the derailleur to move? Really need more info.

Start from scratch here and see what happens.. http://bicycletutor.com/adjust-front-derailer/