my dishwasher won't get things clean?

my Bosch exxel auto dishwasher is not cleaning items well at all. In fact, some are coming out as dirty as they went in. I have run it on a programme with a dishwasher cleaner but it hasn't made a difference. The filter appears clean. The machine is about 2 years old and came to us as a hardly used second hand hand machine with no instruction booklet.