help in resetting build.prop file permission

Hello guys. Today i was replacing my edited Build.prop file (which i edited to change my model name) with original one. But after that i did a big mistake, I changed its permission and restarted my phone.. And now its not restarting. it Please help me.
I dont know much about ADB and CWM.(i never used them)
I have back up of Build.prop in my External sd.
(sorry for poor english)
Thanks:):)