Need help on Daewoo microwave oven

Question

We recently acquired Daewoo Microwave oven with model KOR 131G. However, after several uses, it doesn't seem to heat the dish, which defeats its purpose. We dont have the manual as i think it was misplaced when the item was shipped. Please help us solve this problem. We don't know what's wrong with it. It still has power though but it wont heat the dish. Was thinking it might be the program as it is digital.

Appreciate your help.