ArcMap 10: Labels not appearing

i'm working in a stand-alone application using arcEngine , arcSDE geodatabase , VB.net so my problem is that i can't appear the features label for some featuresClass. when i opened it in arcMap to test it, despite Labels are set in Properties, layers are checked to label in the TOC,I'm unable to get labels to display in Arcmap 10.
i'm not looking to change my mxd file. all feature classes are in a geodatabase.
:( :(