W2K mouse freezes locking PC

1 out of 10 times, my mouse freezes while scrolling down using the “down arrow” button only. It never locks scrolling up, across, or down using the slider bar, only the “down arrow” button on the lower right-side of my screen. Once the mouse freezes, the PC is locked-up completely. Cntrl-Atl-Del is of no effect, etc. Cold reboot is always necessary.