I forgot to mention step 6:  Creating a new profile Or moving you mod folder.  It really varies slightly based on the mod system you use.

Step 3: Delete Fallout 4 from (steam or other) and the Fallout4 folder located in your My Games folder on your C : drive
Step 4: Download a fresh Fallout 4 (Optional copy and paste so you wont have to download a clean version for future builds.. I see you "I followed all the steps and nothing works" 'points at own eyes then at yous' !!

You cna just rename Failout Folder to something else like for example "Failout Old Setup" and then Verify Steam Files for Failout...

If Steam is unable ( and will be after u rename folder ) to find Failout Folder then Steam will start to downloading all files

This way u don't have to copy old files u just rename them :x... its much faster

u skip Copy process and Delete Process...