Hi,
If you are using a Mac laptop with an external monitor, try opening iMovie with the laptop lid open.
If that's not the problem, here are a few other things you can try:
1. Open iMovie while holding down the Option and Command keys, and selecting to delete preferences in the box that appears. (Do this one first, before trying anything else, because it is easy to do.)
2. Try opening iMovie while holding down the Option key, and then selecting to create a new library in which iMovie will open. If it opens, then you can try copying your projects from the old library to the new library, one at a time, and opening iMovie each time until you hit a crash. When you hit a crash, the last project added will be the one that caused it.
3. Open iMovie in a new user account. You can use the Guest account on your Mac for this purpose.
4. Open iMovie in Safe Mode, and then after it loads exit Safe Mode and reopen in regular mode.
-- Rich