2) There can be a DOZEN reasons why the file MSVCR120.DLL does not work on your computer. It can be a registry problem, file read error or damage done by virus or malware where the file has been replaced by a virus with the same name, just to name a few.
3) You need to perform system maintenance on your Windows installation by testing System Restore back to an earlier time when it last worked or if you know about any recent changes you can undo by using System Restore. Also, your system Registry may have corrupt entries for MSVCR120.DLL so you need to re-register that file in your Registry, even though I have no idea whatsoever if that is the case on your computer.
4) You either need to read and try out different suggested solutions from various help sites to fix your issue, or consider reinstalling Windows completely. (Yes, I know it takes a lot of time, but it is neither easy to know exactly what is wrong nor to fix your issue. There are no simple, single solutions to this problem.)