Hi,
Crashes can be caused by a number of things.
Try booting up in Safe Mode (see Finder menu for instructions) and, after everything loads, immediately reboot in normal mode. Now see if you can open iMovie.
Also, update to the most current OS and iMovie that you can. If you have already updated iMovie, try redownloading it.
If still no luck, here are a few other things that you can try, excepting nos. 4 and 6.
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.
-- Rich