Microsoft wireless laser mouse 6000

So I have this Microsoft wireless laser mouse 6000. It is actually a keyboard/mouse combo. The keyboard is the 6000 v2.0, but the mouse is just 6000. I just built a new PC: Asus P5N-D nForce 750i SLI Socket 775 Motherboard Intel Core 2 Duo E7400 2.8Ghz 3MB 1066FSB CPU OCZ SLI 4096MB PC6400 DDR2 800MHz (2x2048MB) and a Corsir 650w PSU. So I installed the Intellipoint 6.0 and updated the sw. The default settings are that the large thumb button goes "back" or to the previous page in an internet browser and the small button magnifies. So I have it set to default settings in mouse properties. I have tried setting the mouse by selecting wireless laser mouse 6000 and wireless laser mouse 6000 v2.0. All the buttons work except the small and large left thumb buttons. I have tried assigning different functions to those 2 buttons, but they will not work with any function. Before this new pc, those buttons worked fine. I'm running XP Pro sp3 and I'm out of ideas...