samsung hdtv channels disappeared.

hi all. sat watchin cbeebies with daughter when screen went blank. switched over to another channel and that too and every other was also blank. on the menu page i tried to rescan for channels but im not getting the option as the page is only on for a fraction of a second before reverting to the earlier, also tried the plug and play but its greyed out so that too is inaccessible. any help greatly appreciated. thanks in advance.