I would first try to clean the preferences, as that seems to help when things get crazy, like you are experiencing.
Get the free Pref Manager software (it can backup your FCP X preferences, so that if clearing them does not solve the crashes, you can easily put them back the way they were).
Also, since you say you import and the clips get red with the exclamation mark, I would check to see if your import settings agree with your playback settings. For instance, you may have it set to use proxy media for playback, but not create proxy media on import; this will have the result you're describing. If that is so, note that you can change the settings, and you can also create the necessary proxy (or optimized) media at any time.