MS wireless laser desktop 4000

Stupid, probably easy, little question. Can't seem to get my computer to recognize the desktop receiver 3.1. I've downloaded (and installed) the intellitype and intellimouse 8.0 software that MS says is the correct software, but still nothing. When I plug in the receiver, all 3 lights flash, but don't light when I try and sync. When I reboot (while plugged in), I get a message that it's an unknown usb device. It came with a comfort keyboard 4000 and laser mouse 5000. I am using the mouse with my old receiver, but would like to be able to use the new keyboard as well. Previous configuration was wired keyboard and wireless optical MS mouse (explorer 2.0) with Explorer receiver 2.0. Do I need to uninstall something before installing the new receiver? Thanks in advance, any help appreciated.