protein skimmer help.

I have a reef octopus classic 90 hob protein skimmer. It's been running about three months and when it works it works great. However, every time I do a water change I have to turn it off as the water level goes below the intake. Restarting it has been the biggest pita. Ever since I got it it never restarts right away. I always had to take it out empty it take the pump completely apart and then it would start. I tried blowing in the air intake and also tapping the pump and cupping the water intake none of that has ever worked. For the last few days all it does is make a humming sound but moves no water at all. Does anyone have any ideas? Nothing is stuck inside as far as I could tell.