Sounds like the same kind of filters I have on my tanks. Yes, they need to be primed. One of mine won't work at full capacity until the tank is full of water, even though the intake is a foot into the water! Doesn't make sense, but it does work eventually which is what counts.
Sometimes the the hole where the impeller sits gets full of mulm and will keep it from turning. In fact, all the parts of a filter (except motor, of course) need to be cleaned periodically to remove all the crap that ends up on all the surfaces. I use a toothbrush (new, never used in my mouth) to scrub things like the impeller and in the corners of the filter. I bought a set of brushes specifically for cleaning the pipes and such.
Then prime, prime, prime with tank water or dechlorinated fresh water to get it going. That just means to pour the water in the "tank" of the filter. Start out by filling it up before you plug it in. Then plug it in and see if it goes. If not then prime some more with it still plugged in. Good luck!