How can i fix my treadmill?

Reebok i run model no REMO-14302BK
The above treadmill runs but when I steps on the running belt stops after a minute or two, the belt will not stop if i don't jump on. To restart the machine i have to pull the safety switch off and on again. The machine has been cleaned and lubricated i have also checked the deck, belt, motor belt tension and condition of the belt which is good. i have also checked the both roller which are rolling freely. My doubt goes towards the safety switch. what do you suggest?