Hi Dick. I'm Greg, an installation specialist, 10 year Windows MVP, and Volunteer Guardian Moderator here to help you.
Having a password but using a 4 digit PIN makes being secure almost as easy as not having anything.
No expert in Forums - where we see the most cases, by the thousands - recommends Avast, AVG. Norton or McAfee, but we have solved many problems over the years by having them uninstalled.
I would uninstall any 3rd party antivirus in Settings > Apps > Apps & Features and try running only built-in Defender which gives adequate protection, best Windows performance, least issues, and is from Microsoft who knows how to protect their OS best.
After uninstalling antivirus in Settings > Apps > Apps & Features, restart the PC, then type Security in Start Search, open Windows Defender Settings, there and in Windows Defender Security Center fix anything that's flagged.
If you want the best on-demand scanner download and install Malwarebytes from https://www.malwarebytes.com/mwb-download/
In it's Settings > Protection > Scan Options enable Scan for Rootkits.
Then on Scan tab choose Threat Scan and Run Scan.
Clean up anything found, restart PC and then run again until it comes up clean.
If you want to keep Malwarebytes as an on-demand scanner then you can disable its Real Time trial version in it's Settings > Accounts tab.
Next check for damaged System Files since the problem anti-viruses can damage WIndows: https://www.lifewire.com/how-to-use-sfc-scannow...
If it cannot repair them see Step 10 here to continue: http://answers.microsoft.com/en-us/windows/wiki...
You should have course have access to your own User folders so I'm betting this is Norton related and that will fix it as it has so many similar issues over the years.
But if not If you have lost Admin rights on the sole acccount then try these steps leading up to if necessary creating a new Local Account which sometimes is the only way to escape Account Corruption in Windows 10:
Right click Start button to open Run box, copy and paste in netplwiz, press Enter.
Highlight your account, then click Properties, then Group Membership tab. click on Administrator, then Apply, OK, restart PC.
If that doesn't help then try this: https://www.kapilarya.com/fix-lost-administrati...
You can also try taking ownership of the affected files or folders to see if this suffices. Use this handy tool that adds Take Ownership shortcut to your right click context menu: https://www.askvg.com/add-take-ownership-option...
If nothing helps try creating a new Local Admin Account to sign into to see if it works: http://www.howtogeek.com/226540/how-to-create-a...
If you can't get the rights to do this then use whichever method works here to enable the hidden Built-in Administrator to be used only in emergencies:
https://www.tenforums.com/tutorials/2969-enable...
https://www.isumsoft.com/it/enable-hidden-admin...
It may be necessary to create Windows 10 Installation Media on another PC to access the Command Prompt without needing a password: http://windows.microsoft.com/en-us/windows-10/m...
Insert media, boot it by powering up PC while pressing the BIOS Boot Menu Key: https://www.sysnative.com/forums/hardware-tutor...
Choose the boot device as a UEFI device if offered. 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.
After it loads, on second screen, choose Repair Your Computer, then Advanced Startup Options, first try System Restore to a point before this. If that fails then choose Command Prompt to follow the step above to access Built-in Admin Account.
Sign into Hidden Admin account, see if you can use netplwiz now to elevate the account. If not try another of these methods: https://www.windowscentral.com/how-change-user-...
If not then set up a new Local Admin Account, sign into it, move your files over, set it up, hide the Hidden Admin Account, when ready delete the old account in Settings > Accounts > Family and Other Users.
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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Standard Disclaimer: There are links to non-Microsoft websites. The pages appear to be providing accurate, safe information. Watch out for ads on the sites that may advertise products frequently classified as a PUP (Potentially Unwanted Products). Thoroughly research any product advertised on the sites before you decide to download and install it. See here for how to try to recover Admin rights: