Original post by: LikeARabbit ,
More than likely the top case connection isn't seated properly. I would disassemble it again and make sure to push this connection in until it feels solid. It's a bit awkward to do the first few times so I wouldn't doubt that it might be loose if you haven't removed the top case a few times. [guide|515|Step 12 in this guide] shows the cable I speak of. [image|326164|align=left] Before re-assembling the Mac I would try to power it on, just to make sure it works before you reinstall all of the screws.