Unable to communicate with Xbee using XCTU, didn't get device serial number
Try to reflash the firmware using below steps


Change the baud rate to 38400 and check "No baud change" under PC Settings in X-CTU
Go to Modem Configuration tab, select correct Modem, Function set and Version
Click "Show Defaults"
Check "Always Update Firmware"
Click "Write"
If "Action Required" window pop up, press the reset button on the interface board once, Digi interface provides reset button.
I'm not sure about other boards. The pop up disappears and module gets programmed to selected firmware.
If you get any errors, like checksum error failed, you need to optimize your interface boards, refer the following link, http://www.digi.com/support/kbase/kbaseresultdetl?id=3418
Now go to PC Settings and change the baud rate to 9600 and uncheck "No Baud Change"
Go to modem configuration tab and select Read, you can see all the XBee parameters.