How do I fix my Windows 10 PC to normal condition after using a registry cleaner without backing up

I used CCleaner yesterday to delete registry entries that generated errors because I was getting a RunDLL error on my Windows 10 PC and I forgot to create a backup beforehand.

When the RunDLL errors popped up again after restarting my PC, I went ahead repeating the same ccleaner actions I carried out earlier, but this time after restarting my PC started behaving weird, like files not opening when I double click on them, windows explorer wasn't opening when I used WIN + E could only open it by opening the folder through sublime text (yes I code), couldn't open a variety of programs, couldn't right click on folders (if I tried, the system hangs).... To cut the long story short, I decided to reset my installation of Windows which fixed most of the errors I got before, the RunDLL errors were gone and everything seemed to work okay, but I have new problems: 1. When I try to extract any file, I get a CRC error when using 7Zip and the windows native extraction just completed but after opening the file I get an error also Unity3d also fails with an error when I try to import packages:Error Unable to decompress package. I detected the CRC errors by testing the file using 7Zip.

Note: I tried re-downloading zips multiple times using different machines and phones then sent it to my PC but still get the CRC error when extracting and have wasted more than 15GB of data in the process. 2. Pictures and media files are not opening, whenever I try I get a 0x800704cf error.

Guys I really need your help cos I'm stuck and frustrated already, used Linux most of my life.

Edit: Ran sfc /scannow and after restarting somehow zips sent to my PC are successfully extracted without errors

Many sites suggest that using "Registry Cleaners" is dangerous!

CCleaner is not so aggressive on registry cleaning like many other registry tools. I have used it without problems. But in general Microsoft does not recommend any registry cleaner (I think, they had one and then discontinued it).

I do not use any reg cleaner in Windows 10 and do not recommend using ANY cleaner at all. Windows registry holds crucial system information and can handle existing errors in registry (like broken links to files, missing programs etc.) by ignoring them!

If a DLL is missing - find software that it belongs to and reinstall. Googling for missing DLL will list sites which supply list of products that DLL belongs to.

Solution to fix registry:

See if you have a recent "Restore point" and do a restore (registry will be restored to an earlier state - you have to eventually install again some software product).

Alternative:

Do a Refresh with keeping files and installed programs (maybe you have to reinstall some software which will be listed by the restore operation)