No way for us to know. But if your system was crashing, there definitely was a problem. The FCE error message you got normally indicates the FCE project file has been corrupted. This probably happened due to whatever caused your system to crash & shutting down the system.
First, make sure your system is running correctly. Then, use the Finder to navigate to /users/yourusername/Documents/Final Cut Express Documents/Autosave Vault and find the most recent backup copy of your FCE project file. Copy the file to your Final Cut Express Documents folder (copy the file, don't just move it). Then double-click the copy to open it in FCE. It should open ok, but will probably not have your most recent edits (transitions). You may have to rebuild the transitions, but at least you will be back in action.