Debrus

I have just had my 8 month old D5100 repaired for autofocus issue and I haven't had it back a week and now it is giving me a No memory card in camera error messge and also on the left top corner of LCD screen in red DEMO with a line thru it. Can anyone tell me if they have had any similar issues? I am taking back to place I bought it tomorrow for some more help. Thanks.