Step stuck.

My step will not retract fully, l have had a look at it but can’t see anything obvious. 
If nothing else does anyone know how to silence the alarm?

I had something similar after the winter break. 

When I pressed the button it wouldn’t go all the way in. I had to push it the last few inches, but it would come all the way out. 

Quick spray of WD40 and a couple of in and out motions and all was resolved.

You can remove the step, strip it down and re-grease everything and ensure the 'closed' switch is actuated. It's an easy job, no special tools required.