I have the same problem as described here in 2011: https://github.com/psychopy/psychopy/issues/90
Instead of appending (or prepending) the PsychoPy2 path to the PATH environment variable, it writes over the variable, causing other programs to break because DLLs and EXEs can no longer be found.
Could it be caused by to long paths like in the old version in 2011?
Windows 7 Enterprise x64
Partial network installation like http://www.psychopy.org/recipes/classroomInstallation.html