1. What version of OSX are you on now?
2. What version of iMovie are you on now?
3. When did you notice that it disappeared? What happened?
4. Did it disappear from your dock? If so, it might still be in your Applications folder. You can start it from there.
5. If it is not in your applications folder, you will need to reinstall. It would be helpful to know the answer to 1 and 2 above so we could give you advice.
thank you its completely gone from applications and my desktop where it usually sits,
i did have version imovie 11
and my macbok pro version is osx 10.6 update 12
its not letting me install imovie the message says
imovie cant be installed on macintosh hd because mac osx version 10.7.4 is required.
but i cant seem to update it
Go to App Store to Purchases tab and download from there.
The current version requires OSX 10.7.4 or later. If your Mac will run it, you can upgrade to Mountain Lion (10.8) in the App store. That is the best course. Mountain Lion costs about $20.
If you want to stay on 10.6, and if your Mac will not support ML, you may be able to contact Apple and request a back level of iMovie that will run on 10.6.8. Probably 9.0.4 would run. There is a Contact Us link at the bottom right of this page.