It used to be in Programs & Features along with everything else you've got installed, but it looks like Microsoft rolled it into Windows at some point not too long ago.
If sfc /scannow didn't fix, you can try disabling it by going to Add or Remove Programs -> scroll to bottom and click Programs and Features. A window will pop up with all the programs you have installed; on the left side go to "Turn Windows features on or off". Click that, and then untick all the .NET stuff and reboot. Then go back into it again, tick them and reboot again.
If that doesn't fix, format drive and reinstall Windows
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