How big is that tank you have? It's possible that the skimmer is broken, considering i haven't heard any good things about the nano skimmers. But then again, i haven't heard any bad things either. It could also just be that it is still breaking in. I have seen skimmers break in at two weeks.. so i guess anything is possible.
By the way, when i was setting up my skimmer, it was overflowing with water just as yours is because i didn't have something that was creating bubbles.. which would be an airline tube in my case. Are you sure you have everything hooked up correctly?