Q: My iCal is not working because of El Capitan

Hi there Seppojm,

It sounds like you are unable to open the Calendar app on your computer. I would start by booting to safe mode and seeing if it will open there:

Try safe mode if your Mac doesn‘t finish starting up

Follow these steps to start up into safe mode.

1. Start or restart your Mac. 
2. Immediately after you hear the startup sound, press and hold the Shift key.
3. Release the Shift key when you see the Apple logo appear on the screen.

After the Apple logo appears, it might take longer than usual to reach the login screen or your desktop. This is because your Mac performs a directory check of your startup disk as part of safe mode.

To leave safe mode, restart your computer without pressing any keys during startup.

If it does, then leave safe mode with a normal restart and make sure it keeps working. If it doesn't work there then make a new admin user on your computer, log into it, and test this again. Let me know how hat goes:

1. Choose Apple menu > System Preferences, then click Users & Groups.

2. Click the lock icon  to unlock it, then enter an administrator name and password. 

3. Click the Add button  below the list of users. 

4. Click the New Account pop-up menu, then choose a type of user.

    
    
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     Administrator: An administrator can add and manage other users, install apps, and change settings. The new user you create when you first set up your Mac is an administrator. Your Mac can have multiple administrators. You can create new ones, and convert standard users to administrators. Don’t set up automatic login for an administrator. If you do, someone could simply restart your Mac and gain access with administrator privileges. To keep your Mac secure, don’t share administrator names and passwords.

      

5. Enter a full name for the new user. An account name is generated automatically. To use a different account name, enter it now—you can’t change it later. 

6. Enter a password for the user, then enter it again to verify. Using a password hint is recommended to help the user remember his or her password. 

7. Click Create User.

From: OS X El Capitan: Set up users on your Mac

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Wonderful! Thank you for the update, I'm glad you were able to suss out the issue!