That issue is difficult to diagnose from here because it's impossible to see exactly what happened when you took the computer apart. In general, however, dissecting a computer without the proper equipment to protect it from ESD can cause it to malfunction. Electrostatic Discharge can cause damage to sensitive components that is microscopic in nature and undetectable to the naked eye.
Your best bet may be to take it to a technician who can run some diagnostic tests and see where the problem is originating. If the price for the repair ends up costing more than the laptop is worth, I would get a new one.