Ps3 no display from av or hdmi

Took my backwards compatible ps3 to a shop for a no display issue. (I had tried both a/v cables and hdmi to no avail.) When I got the console back they forgot to give me my HD and that should have been my first clue. Secondly they didnt clean up any of the vents which I guess I didnt ask for but I thought they just might do that. Anyway I get home and use it for about a week before the same issue happened. They said they will fix it again for the same price but obviously I dont want to pay them again.