For guidance on debugging an installation, see Frequently asked questions.
Problems with git#
First, make sure you have a clean build and install (see How to completely remove Matplotlib), get the latest git update, install it and run a simple test script in debug mode:
rm -rf /path/to/site-packages/matplotlib* git clean -xfd git pull python -m pip install -v . > build.out python -c "from pylab import *; set_loglevel('debug'); plot(); show()" > run.out
Of course, you will want to clearly describe your problem, what you are expecting and what you are getting, but often a clean build and install will help. See also Get help.