problem in xbee s3b detection in xctu 6.3.1

, , , ,

I have 2 xbee pro s3b dmst module 900 mhz. Initially I made a connection between the two and made them talk.
But now one of my xbees are not at all detecting in xctu. I used an explorer dongle for connecting xbee to mu PC. And the dongle is working properly except the xbee.
Can u help me with solution. It is kind a urgent.