I was following an SDL tutorial, and it all was going okay up until I had to include some new directories in the SDL files regarding textures. After this, I got a hell of a lot of errors(626 in all), and I realized they are all coming from the CMath file. I scrolled all the way to the top and realized that Cmath is unable to open math.h. I have no idea where to go with this, or what the problem could be.
Alas, I'm too impatient to watch an 18 minute video through, and I have no interest in playing with DropBox just to get at that Dev.zip.
For now, the way to figure out what went wrong is to roll back to a point where you last made changes that did not break the build.
From that point forward, pay close attention to what could have happened. When you discover the thing that causes the breakage, analyze it.
Have you moved files around? Changed the directory structure?
MSVC is a little unique about how it handles library and header includes -- you must explicitly add each external item to every project you do. (I do recommend keeping include, bin, and lib folders under C:\Users\Public\Documents\Visual Studio\ and/or C:\Users\moosymann\Documents\Visual Studio\ for your common libraries and adding it to the IDE's "include these directories automatically" options, but that seems oddly rare in MSVC-land compared to everyone else.)
A project file cannot keep things in absolute paths -- otherwise once you give someone the source to your code they wouldn't be able to compile it -- so all the project files are relative. (Warning -- that was a simplification.) What it means, though, is that you can confuse the compiler by moving things.
I think this is the most likely what-happened. But without a more direct hand in your code, it is just a guess.