Windows Unusable After Extending the Environment Variable to More Than 2047 Characters#
On Windows 7, the maximum length of the environment variable is limited to 2047 characters due to a bug in Shell32.dll. This may be triggered by any software installation that tries to extend the PATH environment variable.
No environment variable should be longer than 2047 characters. If there are variables longer than 2047 characters, variables after them won't expand, won't show up, and the PATH variable will become null.
Exceeding this limitation causes a broken Windows installation. Windows can be repaired with the Last Known Good Configuration boot menu reachable by pressing F8 while booting up the computer.
Solution#
A hotfix can be downloaded here.