The incline doesn't work on my EKG 770?

I just got this from a friend. I got the incline to work great one time, (by accident I think). But now I can't get it to go past a 2.5. I have tried every program and it just won't go any higher. I don't know how I did it the time I got it to work. I printed out the manual but it doesn't help. It just says to select the program and it will do it on it's own. Not in my case. Any ideas or help?