>>I can change it, but only when logged in as the default Administrator account on the domain; I can't change it when logged in as a domain admin. Try making the change while logged in as Administrator.
>
>I am the Administrator. But I also tried logged on other accounts. Nothing works...
>
>Finally, I changed the mouse (physically, the device) with an old one. This way, I could change the driver to MS Serial Mouse. I've put back the Logitech mouse and reinstalled the driver for Logitech. After I reboot, again, the Change button is disabled and the name of the driver is "Unknown". But, probably, the driver is ok only that it doesn't show it correctly. (Logitech doesn't provide drivers for NT and recommends to use the ones that come with NT.)
>
>Still, I don't like how it "moves" and there are some features I can't use. Anyway, it's not very bad. It works well enough. :)
>

Is this the same machine that's giving you trouble with MAPI and the fax software? If so, maybe something got hosed. I'd look at running an NT install using the Repair option, followed by reinstalling SP4 and the Option Pack if you use any of its features.

If you do install SP4, and you're running an AGP video card (the ones I've been bitten by have been the Matrox G200 and The DIamond Viper V330 and V550), load SP$ before running the manufacturer's video driver install. The Matrox card in particular locks up in odd places once the actual SP4 install starts (in at least one case, I had to go back and do a complete reinstall of NT after an abortive partial SP4 upgrade) and SP4 simply refused to install at all with the Diamond drivers in place. In both cases, reverting the drivers to Standard VGA (or using the straight VGA boot) allowed SP4 to install, and reinstalling the video drivers after the upgrade went smoothly.