What is the difference between safe mode and a clean boot?

That's quite a good question!First of all, Safe Mode pretty much disables everything that isn't necessary for Windows to start. So the remaining services running are running at their most stable while accelerators are switched off (ex: video accelerators).This way, Safe Mode helps you to address hardware-related issues and sometimes certain software issues where Windows is prevented from starting up correctly. if at all.On the other hand, clean boot's main purpose is to address software compatibility issues. It starts Windows normally but disables3rd party applications that usually load on start up. Such applications may be the antivirus, certain system processes, Skype, etc. In order to access Safe Mode, you will need to reboot your computer and press F8 during the boot process. While to access Clean Boot you will need to go through the msconfig menu while Windows is running.I hope my answer helps! 

Well said Sir Rashed.Thank's a lot for your answer on my question.More power!