Hi nmcampb
An MBR error indicates there is a problem with the file system on your hard drive
Start your PC, just as Windows attempts to load (spinning dots), press and hold Power Button for 5 - 10 seconds to perform a Hard Shut Down
Do this twice
On the third start Windows will boot into the Recovery Environment and from there you can access System Repair, Safe Mode, Command Prompt . . . etc.
Choose Command Prompt
Run this command and hit Enter:
bootrec.exe /fixmbr
Then when that completes, restart to see if your PC will boot
If you cannot get into the Recovery Environment, you will need Windows 10 Installation media and use that to get into the recovery Environment by choosing 'Repair this Computer'
Then go into Command Prompt and run that command . . ..