My samsung ue40b7020 lights up but no picture

you may need HDMI cable to see video.

You might want to make sure the HDMI cable is fully plugged at both ends of the cable and try a new HDMI cable. A marginal cable will occasionally drop out the picture.

Is the captioning coming from a source such as a Sky box? If so, you need to switch off closed captions on the source box and not the TV.

Back-light problem. Check and replace damaged component/s at its back-light inverter board, or replace this board as card basis. If you wish to get some details; check the site linked here. Surf the site with patience. Pull up older posts. It will be best to replace the inverter board as card basis.
http://electronicshelponline.blogspot.com/

Refer its user manual for connection details. Electro help

Back-light fault. Contact any service technician. If you wish to get some details; check the site linked here. Viewing it in "Mosaic" or "Magazine" will make surf easy. Pull up older posts. Surf the site with patience. Do a search by type in the brand name of your device at its search box and press "Enter".
http://electronicshelponline.blogspot.com/

You have set up your tv in store (demo) mode. Go to settings then plug and play and scan channels again but this time select home mode before it searches for channels.

http://sky.uebv.com/ put details in here

Try 1340