Before you go to take apart the computer be sure that the drivers for the hardware are installed and/or working properly. You can see this in the Device manager by right clicking on the windows button in the bottom left hand corner, then hitting device manager. From there go under keyboards and your keyboard should be listed there. If everything is all well and good, then I would leave you with the iFixit guide, but there is none at this time. I will report back later if i find a guide to help you. -Jonathan (EDIT) I have found a disassembly guide. If it were to be rated on iFixit this would be about a hard. Here ya go! http://www.myfixguide.com/manual/lenovo-yoga-3-pro-disassembly/
It could be a problem either with the display outputs on your logic board or it could be a software issue. Did you try to restore an earlier time machine backup? If you don't have time machine, try a fresh install of MacOS. As others suggested It could be the result of liquid damage on the logic board, but you mentioned it only suffered some bumps and drops. Have you opened the bottom of the computer to see if there are any loose connections?