Solution tried so far by me
1. I have erase external sd card in mobile itself.
2. Reset the entire phone.
3. Uninstalled the mmx driver on my PC and reinstalled it.
Guys recently I started using 32GB card with my MMX CHD and everything is working only for when I try to connect my mobile to PC for file transfer via usb storage I can see only two drive one of CD drive of mmx and other internal sd drive and I can see one more drive but it is not mounted which is my external sd drive when clicked on it, it asked to enter disk guys plz help.