I have had this happen in the past, removing the top of the unit (although different model to yours) was simple. It took no more than 5 minutes to repair.
Both times this happened, the culprit wound up being that silver ring/decal you often find centre of rented dvd's. One time it was barely peeling and wound up stuck; the other, part had come off and the gum/glue wound up attaching itself to the dvd drawer.