Please make sure you meet the minimum requirements: http://blog.ubi.com/far-cry-4-pc-specs/
If you've done this, please make sure all of your drivers are up to date and that you verify your Uplay game files for Far Cry 4: https://support.ubi.com/en-US/FAQ/60...0000000ee85CAA
If the following steps do not assist with this issue, please contact our Ubisoft Support for further assistance. Thanks. http://support.ubi.com