I have a new Samsung 65" tu8000 that I purchased 3 weeks ago. When I turn the tv on all I get is a black screen were you can faintly see the menu and app icons if light is shined on the screen otherwise it look dark as if it's not on but you can hear sound just fine. Should have this issue on a brand new tv. Tried unplugging it for a few minutes, disconnecting/checking hdmi connections, etc. still nothing...
When your TV has a black screen even when it's on, it's quite possible it could actually be your external device and not your TV. If your TV is connected using a One Connect Box, there are a couple of extra steps to troubleshoot.
·Press the Home (Menu) button on the remote.
Confirm the TV is set to the same source as the external device.
Test the HDMI cable.
Test different external devices.
If there is still no picture, use the following link to find a list of service centers near that can do the warranty repair. http://www.samsung.com/us/support/service/location
With it being only 3 weeks old I would recommend getting in contact with the local retailer for some options.