Hi, thank you for contacting JustAnswer.com. My name is Russell. I will do my best to provide the right answer to your question.
I would try a incline calibration operation, at this point, in case the problem is one of the electronics, rather than a mechanical linkage jam-up.
Also, have you tried turning it Off, waiting 20 minutes with it unplugged from the power, then turning it On again? I would advise trying that too.
I think the linkage is likely to be defective... or perhaps, the position sensing.
But there could be a number of problems that cause the defect, at this point.
Would you think it well to turn the problem over to a repair-service co. local to you? if so, please tell me your local zip code, and I will research and cite some for you to contact.
Very well. Would you like to close this case now, or wait until you hear what they suggest?
Note: if your treadmill is less than a year old, it may be covered by warranty for free repairs... in your region, of course, since shipping it off would be quite prohibitive.