Dell Inspiron 3650 Desktop Windows 10 Windows Defender constantly rebooting

Malwarebytes Antivirus was added to the computer and it detected a problem. I rebooted using the Windows button rather than thru Malwarebytes. Windows rebooted to Windows Defender which runs, gives an error Stopcode 0xc000021a and then reboots and repeats the cycle over and over.

I used Dell Windows 10 disk and I tried to restore the system to earlier states and received error code:

0x80070005 Advanced-System Restore did not complete successfully-files not changed. Could not access a file-antivirus program running-disable antivirus-retry.

Safe boot mode is unavailable. My command line skills are limited.

If possible, I would not want to reinstall Windows 10 because I have numerous downloaded programs and am not sure of the passwords.

This stopcode usually means that there is a problem with some of the main Windows system files being damaged, sometimes caused by viruses.

What I'd suggest is two steps:

1. Run an antivirus on the PC (it does give you some time to work before it crashes?). Then also run a boot-time scan with an antivirus that has this capability.
2. Since Windows is already damaged a good thing to do is perform a repair via an in-place upgrade. (which basically reinstalls Windows but keeps the programs and files, just like when upgrading an older windows to windows 10.) A good guide for that can be found here: How to Do a Repair Install of Windows 10 with an In-place Upgrade (the Step 6 method is probably easiest.)