panasonic Viera VGA Port

I recently put my TV on the wall and up today was running my lap top through the VGA port on the TV  i have ben doing this for  2 months quite happly

when today The vga port worked no more on the TV.  Just black screen with pc in the corner

How do i know its The TV

We have a second Viera in the bedroom I plugged the lap top using the same Vga lead into it and it works no problem

So can anyone advise   whats happened . is it  going to be expensive  Have I unknowingly damaged the TV in running the laptop through it.