dg250dtra08?

I have a DG250DTRA08 ,have tuned it all in looks great , until I turn over then goes blank at the front except for green light and on my tv it says no aerial, so I switch of and on and its ok , have checked my aerial and scart both ok , as I have tried another freeview box on to check , any ideas , I bought about a year ago but never used it so out of warranty cannot take back to shop, want to get rid of my sky plus , so would love to be able to use this box , thank you