Thank you for the post.
I do not receive any errors when opening FileMaker Pro 12.0v4 on Windows 8. Either the FileMaker installation or the Microsoft Visual C++ installation may be corrupted.
Uninstall FileMaker Pro 12 and all versions of Microsoft Visual C++ from Add/Remove. Afterwards, reinstall FileMaker Pro from the latest version of the full installer located here:
The Microsoft Visual C++ required by FileMaker Pro 12 will reinstall during the installation. Please keep me updated with any progress and report back with the results.