Dryer stopped working on my Hotpoint WD640?

I have a Hotpoint Aquarius washer dryer WD640 which used to work fine but now when I use the dryer the clothes come out as wet as when I put them in, you can feel the heat through the door when it is on and when it's finished the towels feel quite warm but really wet even when I've set it for 2½ hours or automatic and I never over load the machine when I'm drying, also a couple of times lately I've noticed beige marks on my white washing, I wasn't sure if this is connected (thought it might be rust marks) although the machine is only 2½ years old.