I have an Insinkerator 1/2 hp disposer that is no longer working. The motor hums but that's about all. I tried using the allen wrench under the disposer and resetting the power button. The water that backs up in the sink will eventually go down after it's turned off, but no food waste. I don't know how old the disposer is, but it was in the house when we moved in eight years ago and it looks kind of rusty. Does it sound like I just need to replace it, or is there something else I should try first? Thanks in advance for any assistance.