Black screen tv but sound?

My mom bought an APEX flat screen tv on Black Frdiay which is only a month ago and now the tv screen is black when it is on.....the sound still there however. She threw away the receipt, thinking the tv will lasts at least a year or so....didn't bought warranty either. So what should I do? How much is cost to fix it?? OR better what is the problem???? Can i fix it myself?