Transitions not working in fcpx.

Suddenly I've noticed that all of my transitions aren't working any more. All that happens is the screen goes black for the duration of the transition that I try to apply.
I've tried starting a new project, getting rid of preference files and other things that have worked before. Any ideas on what's going wrong, I feel like somehow it's missing and fcpx can't load them.

New one for me. Have you tried a reinstall?

No I have not as it's a bit of a pain to do as I don't have easy access to the apple account linked to it.
Is there a way to trash all the plug ins and stuff for fcpx and keep the app because I remember installing it and then fcpx downloading all the additional content.

Alright I think I've found the problem finally. There are no files in the transitions folder???? I downloaded a few custom ones to see if putting some in there would work, and those ones work. Is there a way to download them again?

The built-in effects, transition, etc, are not in the Motion Templates folders.

Try getting the free app "Preference Manger" from Digital Rebellion. Use it to trash the FCPX pref files. That may help. You won't lose anything running it.