someone please help

Hi everyone i'm having a nightmare with my tv i've plugged my freeview box into the scart socket and it lets you watch it but then every couple of minutes the tv will switch itself over to av1 then back to av2 which the box is plugged into,i've tried putting it into av1 but it still does it i cant watch any programme from start to finish and its driving me mad!! We bought it off a man and he said he'd never used the av sockets and seemed genuine as he wants us to keep him updated,you can watch a dvd fine with the dvd player plugged into av1 or 2 and it doesn't do it.Can any one help? or had the same problem? the model number is KV-32FC60/Z