That might suggest that there is a piece of software (driver, service, process or application) that is running at startup under a normal boot that is not running at startup under safe mode boot.
While in safe mode....
Launch task manager and use the startup tab to disable all startup items. While in task manager use the file menu to "Run new task" and type msconfig.
In msconfig use the services tab, check the box that says "Hide all Microsoft Services" then use the disable all button to disable the remainder from starting at startup.
Reboot normally.
Basically you're performing a clean boot as described here
https://support.microsoft.com/en-us/kb/929135
Easily done and just as easily undone.... just DON'T mess with the Microsoft Services. Again, check the box that says "Hide all Microsoft services".
NOTE: This may or may not impact some third party security / antivirus suites and if that is what is causing your boot issue, then you may have to physically uninstall those, including running their vendor specific and proprietary removal programs to get rid of those completely.