So I got skyrim for christmas for my new PC, and I was installing some mods today. The game seemed to work perfectly fine when using this mod loadout: iHud, SkyUI, TESV acceleration layer.
But I added these few mods and suddenly it stops working. When I launch through steam, it says "Skyrim Launcher has stopped working" and when I launch it from SKSE loader through the NMM it says "The program can't start because d3dx9_43.dll is missing from your computer. Try reinstalling the program to fix this problem.".
I tried defragging the files through steam and also verified the game chache and reinstalled and did the same again. Still doesn't work. Please help?

In this case "reinstalling" is referring to Dx9.

How would I go about this?

Sounds like some mod is relying on the D3DX utility library for Direct3D and you don't have the latest DirectX installed properly. The game itself depends on d3dx9_42.dll and not d3dx9_43.dll (Microsoft never bothered to spec these utility functions so there's a ton of different .dll files for them). Try running the http://www.microsoft.com/download/en/details.aspx?id=35.

If you're having trouble removing some graphics mods, note that some of them do not alter any game files. Instead, they plant their own "Direct3D" .dll files in the game's folder, making the game use them when it tries to load up Direct3D. This isn't detected by Steam's file verification since no actual game file is modified, and to remove such mods you have to remove the d3d9.dll from the Skyrim folder.

Hoorah! That last detail about the d3d9 fixed it! Thanks so much!
It must have been my FXAA mod that i installed earlier today.

I also was getting this fail. Any idea what caused this....I did install the FXAA Tool as well. However, it did work. Once I deleted that .dll file game came back. Unfortunately, I have deleted everything relating to game to fix the problem, thinking it was something associated with mods. Now I have to start over from scratch.../sigh.

You would think that Skyrim would provide you with those DirectX files... They are, after all, required and arn't included in DirectX 11(or even 10).

Also had the same error message when I installed FXAA today. Downloaded the DX9 setup from Microsoft, installed and everything worked fine thereafter. I Googled D3dx9_43.dll and found the answer at About.com PC support. I like to read about why applications are not working properly on my PC and fix them.

If the game was working without some mod installed, the .dll file is only required by the mod and isn't really Skyrim's responsibility. Steam does install some libraries whenever you start a game for the first time to make sure at least the basics are installed.

The files are included in the latest DirectX installer, but many games still package old versions of that for some reason. Seems the only way to make sure you have all the different D3DX9_nn.dll files is to get and run the installer yourself.