These units are mass prioduced overseas for the big box stores like Wallymart, K Mart, Big7 etc. They are low quality units compairativly and are not supported by the stores that sell them. No spare parts are available nor are there any service manuals available.
Unfortunatly the best suggestion I can make is to open the unit up and look for a broken oir loose wire inside. If you know someone thast is a good handyperson give it to them and Im sure they can fix it for you.
Although cheaply made these units are very simple in their construction. This makes repairing them easy for anyone with a good mechanical apptitude.