Laptops are relatively easy to dismantle and fault-find.
The key to it is organisation. Lots of little pots numbered from one to infinity minus one for the screws from each stage.
Second, take pics of every stage.
Unlike a desktop, various bits (keyboard and monitor at least) are connected by trapped cables. You need to pull back the clamps (tiny, plastic) with a sharp blade and magnifying glass to disengage the clamps.
I suspect you'll find that a repairman left a screw out, so that something isn't permanently connected. With laptops it is essential that there are no "pocket screws" (left overs after remantling).
You'll have fun taking it apart. In particular, the lid/screen hinge, which you might or might not have to tackle. Getting the keyboard out can be tricky too. But I've done it and they have all worked afterwards.
As I said, you're looking for something missing. My bet is on a motherboard mounting screw.