Without knowing all the details you like so many fail to give i would suggest
format and do a clean install on a formatted drive.. Save any important
files first..
Addition:
Did you upgrade in the past 30 days?
If it has been less than 30 days since you
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, then you can quite easily downgrade to your previous version of Windows.
To do this, open up the Start menu and select 'Settings', then 'Update & security'. From there, select 'Recovery' and you'll see either 'Go back to Windows 7' or 'Go back to Windows 8.1', depending on your previous operating system.
Click the 'Get started' button and the process will begin. You may be asked why you're uninstalling Windows 10 and downgrading to your previous version of Windows. Once the process is complete, Windows 7 or Windows 8.1 will be back.
Has it been longer than 30 days since you upgraded to Windows 10?
If it's been over 30 days since you installed Windows 10, then you won't see this option to uninstall Windows 10 and downgrade it to Windows 7 or Windows 8.1.
To downgrade from Windows 10 after the 30 day period you will need to perform a clean install of Windows 7 or Windows 8.1.