Skimmer help

[Oilers]

I came back from my vacation and found that my skimmer is not working as it has the last couple months. I just bought it a couple months ago and it was working flawlessly. It is a Vertex Alpha Cone 170. Right now, the pump is still pumping but it's not foaming nor collecting waste. The water level is stuck at about half way no matter which way I turn the knob. Can you tell what's wrong with it and how to fix it? Thanks.