I recently updated my iMac 21.5 " from 10.6.8 to 10.9.2 OS X Mavericks. After installing almost all my apps not responding to open. Please help , what can I do, or what I shouldn't do!!
Cristopolo

Sounds like you had a problem running the update. Make sure your data is backed up via Time machine or another method and follow the advise given int this thread from the Apple forums.