Two things you could try doing, or need to do:
1: Download & install the DirectX End-user Runtimes from here: https://www.microsoft.com/en-us/download/details.aspx?id=8109 (do not just un-extract the files, make sure to INSTALL them!) These work on every operating system from Windows Vista SP2 up (including Windows 10!)
If that does not work, skip to step 2, if it does you're done.
2: Redownload/Reinstall the FULL client from here: http://epicpw.com/index.php?page=download | I do NOT recommend using the manual patch method, as you will be missing various soundbytes, and certain instances will not let you out (normally (via portal/s), will have to burn a teleport stone to get out.)