Help please - Whisper? filter will not prime

I have an older filter for my tank. I am pretty sure it is a Whisper system from about 5 years ago, but the person that bought it died a few years ago, so I can't ask to make sure.
My problem is I took the system apart (removed motor, separated the other parts to soak/clean them) and now no matter what I do I can not get it to prime. I am pretty sure I put it together right, and the motor is running, but just can't seem to get it going from there - have tried priming with only a little water, and kept adding all the way to it being full, but no matter what i did it would not start. I am on a major budget right now, and would prefer to fix if possible instead of getting a new one.

Thanks for any help I could get,
Tiffany

is it canister or hang on back?

I'm assuming this is a hang on back. Is the impeller spinning?

Sounds like it's either not creating enough of a siphon (could be because you don't have it together tight enough, make sure it's seated well, also check to make sure there's no cracks or anything in the top of the tube) or the impeller isn't spinning fast enough to suck any water in. That could be because the impeller is damaged or something is creating friction so it can't get going right. Otherwise maybe the motor is bad, it might sound like it's running but it's not enough to run properly.

Try lifting and reseating the tube several times while it's plugged in and the back is filled with water. I've succeeded in getting stubborn filters running many times with that method. Sometimes the tube will either not seat properly the first time or traps air preventing it from priming.
If that doesn't work take it apart again and make sure everything is in right and nothing got in the filter while you were reassembling it (I've had a strand of hair get in an impeller when I put a filter back together before and it was enough to stop it from working).

Other than that I don't really have any suggestions except maybe trying a new impeller. Of course if that fails you're out the money you spent on the impeller, but if it works at least you're not looking at buying a new filter.