Since we don't really know what state your computer is in at this point it may be hard to tell you how to fix it. You can try and re-install Cortana. Open an elevated powershell prompt and type the following
Add-AppxPackage -Path "C:\Windows\SystemApps\Microsoft.Windows.Cortana_cw5n1h2txyewy\appxmanifest.xml" -Register -DisableDevelopmentMode