I'm sorry that you are having that issue. It sounds like it could be an installation problem. Try un-installing and then re-installing the modpack. If that doesn't work, could you please describe the directory (AKA folder) structure of the installed modpack and verify that the various "texture" directories (folders) are not empty?
If you want to verify that your installation is complete, here are the "texture" directories you should find and the number of PNG files in each, assuming you have installed the latest version (1.91) from ContentDB: