My wireless keyboard has stopped being "found" by my computer.

My wireless keyboard still functions fine on my laptop, but not on my desktop. I connected a USB keyboard and proceeded to set it up as a new device, but the setup assistant can't find it even though "discoverable" is checked off.
I have been using this keyboard for a couple of years, so replace batteries thinking this was the problem... but agian it works fine with my laptop.

Help!