OT: Keyboard hasltes

Hi.
I have the Logitech bluetooth keyboard and mouse. I think it's the MX-900.
I've just set it all up, and it worked fine, but on rebooting, the keyboard
no longer works, although the mouse does. I can unpair and pair up the
keyboard okay, but not connect. When I try to, it says the keyboard must be
in discoverable mode, but I can't find any literature from Logitech about
how to do this. The batteries must be okay because I was able to enter the
PIN code as part of the pairing up process. It's very annoying. Any ideas?
Thanks.