What kind of issue are you having, not starting is rather vague. Dose it crash, do you get black screen, or dose it not start at all.
Common issue with black screen is usually graphics spec related like pixel shaders,
if its crashing post the crash report as that's somthing very technical,
if it's not starting at all that's almost always due to a currupt file. And not nessisarly the game files a lot of times between updates your save files from previous updates can get currupted by other games, programs, or malware on your pc. So move your saves out of the save file so it starts up like brand new and if it starts then you know your issue.
If it's none of those, then I most certainly cant help you sadly.