Is it a Laseriffic topper with the screwed on feet ??

If it is then chances are that when the feet have been screwed on from underneath they have poked through and pierced the led strip causing a short .

Remove the screws and the led strip , check it for damage . If it's damaged by the feet screws then it'll need replacing unfortunately .

Before you re-assemble it grind/cut the screws so that they are a bit shorter so it won't happen again .