Exporting h.264 from Premiere Pro resulting in black screen on Windows 7
h.264 has different "levels" of compression.  These levels have to be supported by the particular playback engine.  Windows 7 supports up to level 5.1 via it's Media Foundation library, however your video is encoded with level 5.2.  Since Windows 7 does not natively have support for this version of h.264, it is unable to play the video component.

You can either re-encode with a lower level or you can suggest that viewers either install a codec pack to provide support or use a third party viewer that includes built in support.