Outlook sometimes has issues where the user profile gets corrupted or can't open along with other issues.

A good troubleshooting step is to build a new profile. This will create a new profile, but you can still maintain the old profile in case any data is not synced over and needs to be retrieved.

Once the new profile is created emails are usually re synced within a few minutes.

Here is a quick video on the steps to create a new profile. Text instructions and photos are below.

https://youtu.be/O5uJCYBQKCs

Steps to create a new profile are:

Open control panel

Change Control Panel View to small or large icons if not already set to this.

Click on "Mail"

Click "Show Profiles..." on the new screen

Click "add"

Name the profile whatever you want (this is just for your own reference),click OK

Input your email information to complete the profile.

Select the new profile under "always use this profile" drop down

Click apply, then open outlook again.
Emails may take a few minutes to start appearing. If you need to switch back to your old profile you can go back to the "always use this profile" drop down and change it to the original profile.