So if you have a Windows 10 account and only wish to sign in locally (not create a Microsoft account) then Cortana box pops up asking you to sign in.
To stop the Cortana box keep appearing, try the following:
Disable Cortana in Windows 10 Home
To Turn off Cortana completely on Windows 10 Home press the “Start” button at the bottom left of your screen and type “regedit” then press “Enter” on your keyboard. Copy and paste the below address into the address bar at the top:
HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows
Right click on the “Windows” directory and choose “New > Key” (folder). Enter “Windows Search“. Select the new “Windows Search” folder and in the right panel, right mouse click anywhere in the empty white section and choose “New > DWORD (32-bit) Value“. Enter “AllowCortana” making sure the “Value Data” is set to “0” (zero) Hexadecimal base.

Disable Cortana in Windows 10 Pro
To Turn off Cortana completely on Windows 10 Pro press the “Start” button and search for and open “Edit group policy“. Next, go to “Computer Configuration > Administrative Templates > Windows Components > Search” and find and open “Allow Cortana“. Click “Disabled“, and press “OK“.
Restart your computer, and Cortana should be no more. Instead of “Ask me anything“, the new search box will only say “Search Windows” which seems to be much better now that it doesn’t search the internet for a locally stored document.
How to Turn Off and Disable Microsoft’s Cortana