Safe Mode is a diagnostic mode for Windows that starts your computer in a limited state. Only the basic files and drivers necessary to run Windows are started. This helps us in identifying whether the issue is due to some third party programs conflict.
— from Microsoft
But it should be noted that pressing F8 or “F8 + Shift” might fail to start computer from Safe Mode, which is largely because Windows 10 is designed with a very fast boot procedure. But it’s not bad to try pressing F8 or Shift + F8 at first, and then use Windows 10 installation disc or recovery drive.
Start computer from Windows 10 installation disc or recovery drive, and click Next > Repair your computer > Troubleshoot > Advanced options > Startup Settings > Restart to get the window below if you are using Installation Disc.
Step by Step Instruction for Windows 10
I know this thread is a month old, but in case anyone stumbles upon it like I did, the fix for me was stupidly simple.
1. At the blue screen, click Advanced Options
2. Click Troubleshoot
3. Look for a Startup button, I forget its proper name
4. A list of boot options is displayed
5. Click Restart
6. Upon restarting you’ll be taken to the boot options you previously saw in #4
7. Boot into Safe Mode only