There is pretty limited info about this home theater system DAV-DZ350. There is no mention of playing Blu-Ray discs. Could you be trying to play a Blu-Ray? If it is not playing DVDs that you have previously played then you might have a small piece of dust on the laser or sensor. You can try using a can of pressurized air and blow it in the disc drawer when it is open or remove the cover to maybe get better access (sometimes). Make sure the AC power is unplugged before opening any device.