Can you share what implied the opening of the laptop? Were you getting any error prior to that?
I would also like to know if you have checked all the cable connections and the power supply unit when reassembling the parts.
Since you have opened your laptop, I assume that it's out of warranty otherwise I would recommend you to bring it to the authorized company for repair.
I think, most of the PC repair companies could help you with the issue. Bring it to one of them and tell me what happened.