How to fix PmxEditor not working
If you can use MMD, that means DirectX 9, VC++ 2008 & 2010 are already working.
In addition to that, the PmxEditor author’s troubleshooting guide says to install Visual C++ Runtime in this order:
2010:x86 → 2010:x64 → 2013:x86 → 2013:x64