Xinput1_3.dll Error Message

First off, some of my system specs;

Windows 7 Home Premium 64 bit
AMD Phenom II X4 955 3.2 Ghz
Ati Radeon HD 6570 1GB Dedicated video memory
8GB DDR3 RAM

yesterday I bought Fallout: New Vegas off of Steam. It doesn't run for some reason, and so one of my attempted solutions was to run it straight from the .exe file. So I did, and when I do that, I get "C:Windowssystem32XINPUT1_3.dll is either not designed to run on Windows or it contains an error. Try installing the program again using the original installation media or contact your system administrator or the software vendor for support." I know that xinput1_3.dll is a DirectX file, and I had already downloaded and updated my DirectX several times as an attempt to fix this problem, so I located the file in my system32 folder, moved it, and downloaded DirectX again (I did it using an older version, a newer version, and the redistributible version that comes with the game), and it replaces the file each time, but I still get the error message. So I figured that this is the reason the game won't run, and am looking for a way to fix this error. I have also already updated my video drivers, and my Windows is up to date.