Hi Gerdibird. I'm Greg, 10 years awarded Windows MVP, specializing in Installation, Performance, Troubleshooting and Activation, here to help you.
- The only safe method to change the User Profile folder name in Windows is here: https://www.tenforums.com/tutorials/28375-chang...
If you need to correct or undo the regedit you did to get Windows started, you can extract the registry from Windows using the Command Prompt, mount, edit and then reinsert it into Windows following this method:
https://www.winhelponline.com/blog/edit-registr...
- To access the Command Prompt use whichever method works in this link to get into Repair Mode:
https://www.tenforums.com/tutorials/2294-advanc...
Easiest is to force shutdown by holding in the power button. Do this twice. The third time you power on it should start into Repair Mode.
- It may be necessary to create bootable media on another PC to access Advanced Startup Options. The bootable media has it's own set of files so that repairs or Reset might work better, doesn't require a password, and you'll have it to if necessary do the vastly superior Clean Install.
To create Windows 10 Installation Media on another PC install Media Creation Tool and follow the directions here: https://www.microsoft.com/en-US/software-downlo...
Insert media, boot it by powering up PC while pressing the BIOS Boot Menu Key given here: https://www.sysnative.com/forums/hardware-tutor...
If the media won't boot you may need to enter BIOS/UEFI Setup (pressing key given in chart in link above) to turn off Fast Boot or Fast Startup first.
Choose the boot device as a UEFI device if offered, on second screen choose Repair Your Computer, then Advanced Troubleshoot Options, then:
- open the Command Prompt to try mounting the registry to do the commands from earlier.
- If that fails run System File Checker: https://www.wintips.org/how-to-run-sfc-offline-...
and DISM: https://www.ubackup.com/windows-10/dism-offline...
- If those fail then go back to Troubleshoot Options to do a Reset.
- If that fails choose Install Now, then Custom Install, then at the drive selection screen delete all partitions down to Unallocated Space to get it cleanest, click Next to let it create needed partitions and start install - this makes it foolproof. Everything needed to Clean Install is here: http://answers.microsoft.com/en-us/windows/wiki...
- If you have files that aren't backed up you can use the same bootable media to try to rescue your files using these methods: http://answers.microsoft.com/en-us/windows/wiki...
Your files should be backed up at all times if you value them at all. In the Clean Install tutorial in Step 5 I give the best methods to back up.
I hope this helps. Feel free to ask back any questions and let us know how it goes. I will keep working with you until it's resolved.
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