Hello @john
It would be very hard to help you don't remember exactly the changes you have made in order to revert them. About the changes in the registry *ALWAYS save a copy of the registry as a .reg file in case you need to restore again the same settings before you started changing.
It would help that you mentioned the version of your operating system. In advance, if you are using Windows 10, this can help to restore the "integrity" of the system: https://learn.microsoft.com/en-us/windows-hardware/manufacture/desktop/repair-a-windows-image
About the registry... is it possible that you have downloaded some "Fix it for me" tool from the internet that was promising to "run this program to fix your issue instead of type all the commands on this website!" or something like that? In that case it is possible that you have installed some sort of virus that have corrupted your system. Run an antivirus first of all.
If the system is clean, the best option would be to save all personal files, and reinstall your copy of windows.
Hope this helps with your query,
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