Laptops are not repaired in the same manner as desktops. I use "indications" to see what part it might be such as beeps, lights blinking or even current consumption. Your post is too light to declare what it may be but I reply since I want to share that I have found spare parts on Ebay that are reasonable compared to factory repairs.
Best of luck,
PS. With only what you wrote, a mainboard is a good guess as any.
My laptop will not startup. Screen does not come on nor can I start from a floppy startup disk. Do you think it is the motherboard and can it be replaced.