I bought my treadmill through Craigslist. It worked fine when I check it out, however, since then I can't seem to make the belt move--- if that makes any sense. I did download the owner's manual, but I need a very, very basic explanation as to how to make this thing work. It's plugged in properly-- I hit start-- the displays light up, it makes beeping sounds, etc. . . it goes now where. Please help!