Transmitter XBee not receiving from Arduino

So my set-up is:

XBee on shield on Arduino Mega 2560 (this sends sensor data wirelessly)
to
XBee connected to the host PC, used with matlab

whenever I look at the BytesAvailable, it is always 0

It was working a while ago, but now it's stopped working =(

Can anyone help ??

It was working a while ago, but now it's stopped working smiley-cry

Can anyone help ??

Undo the changes you made.

You seem to have omitted a few details, like the kind of XBees, how they are configured, what kind of shield, the code, etc.