A possible cause to your problem is that the side wheel of the Roomba get stuck. There might be some obstruction preventing the wheels from moving. Try pushing the wheels up and down to get any debris and dirt out and see if the Roomba cleans now. If it still doesn't, the wheels might be dead, so it's best if you replace it. You can try going on the Roomba trouble shooting page to see if they have a solution there. www.ifixit.com/device/iRobot_Roomba_650