Hi, jeverly1113,
Glitches in the version itself would probably need to be addressed by Apple. You could always try to restore your previous version from your Time Machine backup. You might need to restore the earlier library as well, seeing as how you opened, and therefore updated, your current library with the new iMovie version. Back up everything before you start.
Short of restoring a previous iMovie version, here are some diagnostic procedures that you can work through to see if any of them help.
Deleting Preferences
Open iMovie while holding down the Option and Command keys and select to delete
preferences in the box that appears. iMovie will open in a new library. Reopen
your old library to get back to your projects.
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.
New Project
Another thing you can try is to copy your media into a newly created project and see if
that cures at least some of the issues. To do that, do an Edit/Select All, Edit/Copy, of the
media in your project and then Edit/Paste it into the newly created project.
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 and return it to the Applications folder.
Resetting the System Management Controller
Try resetting the System Management Controller:
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
If none of the above help, try calling Apple Support. Click on the Contact Support
item in the upper right of this forum's screen. Navigate to a place where you can
input your telephone number.
-- Rich
