Sounds like a Super Cub LP. I've had that problem with mine. You will need a new reciever. The speed control has gone bad, Ihave searched high and low for a replacement for these but have yet to come up with one.
It is a relitively easy fix if you can find the speed controller. Unfortunately, you are going to have a problem even getting a new RX, as they are on back order until the end of July.

Which is really kind of irratating, As many planes as they are selling it's hard for me to understand why they can't stock the parts for them.

I just recently bought a second one on ebay because I couldn't get a new reciever for my old one and didn't want to wait a month or more before Iflew again.

I have had nothing but good experiences with Horizon Hobby, but not having these parts is a little discouraging, considering there failure rate.