I tried to download a texture pack/mod for sphere worlds, or something. Now when I go to play, I can log in, but when I click my world it comes up with a black screen. Any help? I deleted my minecraft files, that I know of. Remember, this is for Mac, and I play the downloaded version.

If the texture pack is over 16x16, did you make sure to use the HD patcher? And did you make sure you deleted the METAINF folder?

I deleted that folder, yes. I don't care about the texture pack any longer, I just want to be able to play.