Why will my Sanyo LCD led tv not light up?

I have a sanyo 32" LCD LED TV model #dp32d53. The other day I turned it on and it turned on fine showing a gray screen with the channel number but then all of a sudden the screen went black. It still has sound and the screen still works I did the flash light test. The TV has the main board/ power supply/ backlight inverter all on one board. From what I found out online if the screen still works but its not lighting up its probably the led driver/backlight inverter so I ordered a used board from a web site that said it came out of the same model TV with a broken screen. I just got the part in the mail today and changed the boards out but it is still not lighting up. If anyone could please help me I would be very greatful. Could it be the actual LEDs? If so is it a costly fix?