My iPad doesn't turn on and randomly died for no reason

So I was just offloading apps since my memory was full and my iPad was lagging a bit so I decided to restart it. After turning it on, it was alive, but after turning it on again, it just randomly didn't work. I already have gone to an Apple center but said they can't fix it. Can someone tell me why this happened? Is it fixable? Is it expensive? Someone please help me. I've already tried charging it for 1 day d still doesn't work.