Here is a simple tutorial to solve this mystery ones and for all:
If you experiencing black screen after login or for any other reason need to access SAFE MODE in WIN 8 do following:
You are already logged in and you see black screen:
1. Press CTRL+ALT+DELETE (it will bring selection screen up - if not, go to Case 2. solution)
2. Select opting "Switch user" or "logout"
3. Select option RESTART but hold down SHIFT key
4. Now you have options to troubleshoot your system and boot in safe mode
You are on login screen and you have not logged yet:
1. Select option RESTART but hold down SHIFT key
2. Now you have options to troubleshoot your system and boot in safe mode
I hope you will find what is troubling your system and have fun solving it by yourself.