How do uninstall every single trace of Blender? When I start Blender, the console pops up and the Blender windows goes into full screen, but the UI is not loading and the whole screen is gray.

I recently switched my AMD card for an NVIDIA card. I deleted all AMD drivers with Display Driver Uninstall. I installed the latest driver from NVIDIA and Blender could start. But it always crashed when I clicked on the UserPreferences->SystemTab. I deleted the config files in User/AppData/Roaming/BlenderFoundation and I could access the tabs I mentioned above with the internal render. When I switched to cycles, it was working, but clicking on UserPreferences->SystemTab OR the Render tab crashed Blender again. Then I tried to remove every trace of Blender, I deleted Blender with windows remove tool, deleted everything in AppData and also deleted everything in ProgramFiles/Blender. I also tried to delete some Blender keys in the registry and even used CCleaner Registry Cleaner. However, when I try to install Blender again and try to open the program with or without admin rights, I always end up with a gray screen. What else do I need to remove to go back to the settings before I installed Blender the first time, where it was working?
I don't know the exact answer you are looking for but I ave an idea.Have you tried loading a different version of blender i.e. if you were using 2.79b try going back to plain old 2.79. It might help as the version you are 'reinstalling' maybe be running into artefacts within the kernel.