XBee Pro S2B is unaccessible

I’am working on a developement project based on XBeeProS2B. I have a small set of this radio unit for the research and developement, and the things are going quite well but now there is the second XBeeProS2B unit which seems stop working. I’am absolutelly not be able to communicate with them neither through Developer Board nor through an USB Xbee Explorer, nor through the XBEe radio network. Watching the LEDs on the Developer Board they seems to work, the power controll LED lights, and seems to wake up after pusshing the wakeup-button, but they are absolutelly inaccessible for any communication. Not even the XCTU can communicate, or recognise them.
The only common thing is that I have refreshed the original firmware to Xbee End Device Firmware on them, but I did it on the others as well wich are working correctly so I really dont know what kind of exident could happen to these two.
So the questions are:
- Is there a way to detect that there is a hardware problem with them happened by accident or some software failure have been arrised?
- If there is a software problem maybe on firmware side, is there a way to make a fully software reset, wich could solve the situation?
- If there is no proper solution on my side, is there a way to send this radio units back to the factory, and get new ones? They are only a few month young, the guarantee period is active surely.
Thank you very much for your help or tips.

Imre Koloszár

Mount the radios on an XBIB board. Then in XCTU, Enable the hardware flow control function. Then try to read the radios. You may have to hit the reset a few times but you should be able to discover them. Then either change the firmware to Router AT or increase the Time before sleep function so you are on longer.