My wireless sony keyboard isn't working - any suggestions for a fix?

There are two battery symbols that flash - a full battery and an empty battery with a line through it. Both flash. I've changed the batteries to no avail. I've pressed the connect buttons on both the lap top and the usb receiver - no avail. The diagnostic tool on the computer says the keyboard is working fine - but it isn't!

I just don't know what to do next and am looking for ideas.

Its a Sony VGPWKB1 VAIO Wireless Keyboard and Mouse (the mouse works fine - which tells me its not a problem with the USB receiver).

Thanks.