Cannot open iMovie

You may just need to wait longer for the backup to complete. Try opening iMovie and leaving it overnight.

If still no luck, try these diagnostic procedures and see if you can resolve the issue.

Opening iMovie in a new library

Try opening iMovie in a new library.  To do that, open iMovie while holding down the Option key and then selecting to create a new library in the box that appears.

Opening iMovie in a new user account

Create a new user account from System Preferences/Users and Groups and try to open and use iMovie in the new account.

You can use the Guest account on your Mac for this purpose.

Safe Mode

You could also try booting up in Safe Mode (see Finder menu for instructions) and, after everything loads,

immediately shut down and reboot in normal mode. Then see if iMovie works

properly.

Updating iMovie

To update/redownload iMovie 10, drag your iMovie 10 app from the Applications folder into the trash, but do not empty the

trash. Sign in to the app store and open your purchases folder by clicking on your name at the bottom of the app store side bar. You will see your purchases displayed, including iMovie 10. Redownload/update iMovie from there. If not successful, drag your present iMovie app out of the trash (if you moved it there) and return it to the Applications folder.

Resetting the System Management Controller

Try resetting the System Management Controller (but no longer available for the new M1 computers):

https://support.apple.com/en-us/HT201295

Resetting the NVRAM or PRAM

Try resetting the NVRAM or PRAM, although this issue would be fairly rare:

https://support.apple.com/en-us/HT204063

Contact Apple Support

If none of the above resolve your issue, contact Apple Support.  The techs there have the capability of remotely accessing your computer that we cannot do here.  To contact apple support click on the Get Support item in the upper right hand corner of this forum’s screen.  Navigate to a place where you can enter your phone number.

-- Rich

Try deleting the preferences.

As you launch iMovie hold down the Command and Option keys until a pop-up window appears.

Click the Delete Preferences button in that window and with luck iMovie should open normally.

I’m confused. You said in your original post that iMovie wouldn’t open. So how did you even get to your project? A project not opening is a very different problem than the app itself not opening. But, anyway, it’s great that you resolved it.

— Rich

Great. Glad you got it working.

So, what exactly was the problem? From what you said, it looks like it was confined to corruption in some projects or a format issue with the photos?

-- Rich

Ah. I see. Good sleuthing.

— Rich