Check Cortana’s Reminders section

You need to check is if you really have saved any reminders or not. To do that, just open Cortana and then open the reminders section. This will show you the list of reminders that you have set. If the list is empty, then there were no reminders set at all.

Turn the Calendar on

If you are not receiving notifications based on the date and time, it is a possibility that your reminders calendar is off.

• Go to Calendar, search for the settings. In the display, go to Remind me, and tick the checkbox beside Reminders.

Check your Account Settings

• Open the start menu and open Settings.
• Now go to the Accounts section and open it.
• Now open the Family & Other Users settings and then click on Add someone else to this PC.
  
• This will help you in adding a new user to your PC with their Outlook account.

Turn Location on

• Open the start menu and then open Settings.
• Now open the Privacy section inside Settings and now you will be on a new screen.
• Now click on Location and turn it on from the slider.

Run the Apps Troubleshooter

• Go to Settings.
• Head over to Update & Security, then Troubleshoot.
• Find Windows Store apps, and click Run the troubleshooter.
• Follow further on-screen instructions.
• Restart your computer.

Reset Cortana

• Go to Search, type powershell and run Windows PowerShell as administrator.
• When PowerShell starts, run the following command:
  Get-AppXPackage | Foreach {Add-AppxPackage -DisableDevelopmentMode -Register “$($_.InstallLocation)AppXManifest­.xml