You go back to the condition when it worked.
Laptops only have a few parts and it really upsets the new tech when they encounter a failing laptop and it's the motherboard. That's the expensive part unless it's some mass produced model we can get on ebay or groupon. I'll continue along here that MAKE AND MODEL matters in such discussions as those old core 2 models are showing up a lot on the usual outlets cheaper than any repair would be.
Ok. So I cant say i have even the slightest clue as to how to fix this or even get started fixing it because in the 10 years ive worked it i have never ran into anything remotely like this. So hes the scenario i am reinstalling a hard drive in a laptop and it wont see the hard drive so i hard reset it by pulling the battery. to my surprise as i look down at the power button the light is on, and the computer is off. i dismiss it and start the computer and at this point the light turns off. In short computer on Light off Computer off Light on. and it was not doing this before the hard reset.