To reproduce:
1. Open Unity 5.5.x and create new project;
2. Close it;
3. Open 2017.1.f1, and try to load any project.

Expected result: 2017.1.f1 editor opens.
Actual result: Unity 2017 does not open, whole desktop screen turns black. Error for multiple Unity instances appear. ( Check Note)

Workaround1: Open Unity launcher window >> Open control panel >> Network and Sharing Center >> Change adapter settings >> Disable Ethernet >> Go back to Unity launcher and press work offline.
WorkAround2: In task manager End Task "Unity editor".

Reproducible with all 5.6.x; 2017.2.x; 2017.3.x; 2017.1.x versions

Note: error window with black screen attached.