Unable to load nib file MainMenu - *Please help*

Please help me, as I am desperate at the moment.

I have a Mac with Yosemite (don't remember the exact version)

I used Clean My Mac today, but it broke something; after using it, I can't open most of apple applications (I can't open app store, mail.app, safari, infos on this mac it's now working, etc.)

Opening the console, I found that the problem seems to be

24/01/15 17:35:36,253 Mail[468]: Unable to load nib file: MainMenu, exiting 24/01/15

17:35:36,255 com.apple.xpc.launchd[1]: (com.apple.mail.7700[468]) Service exited with abnormal code: 1

This happens with almost all apple application.

All other app work fine; chrome, itunes, finder etc.

I need to find a solution that does not involve bringing the computer to the apple store; I have a lot of exams in these days and I need my mac to study.

Please help!