Problem with MSE error code 0x80070645

[System]

I have tried everything except one that I do not know how to get to. I have run Microsoft Fix it, cleaners etc, and each time this stupid error code comes up and I have about had it. I uninstalled MSE in hopes that would work, and of course it didn't.
When I go to re-install I get same error code. I need step by step in layman terms how to get to the HKey class root (registry) to clear this so I can get MSE to reinstall. Thank you

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