I agree - definitely sounds as if your presser foot is preventing the fabric's transition through your machine. If you've still got your machine set on the last sewing you did - two pieces of cotton fabric? - then it's unlikely to cope with all those extra layers in the same way, even with a walking foot.
To check if it's the walking foot, keep it on a 'normal' presser foot setting and try to sew two pieces of cotton and watch the walking foot teeth to see if they are moving. If they do, then it's your presser foot pressure. Good luck!