r u on WIndows XP?
if yes, XP has some problem with Logitech Drivers. best is to:
enable ur system restore (as I have disabled it) and then install mice drivers (logitech specially), if it works, fine, else restore, and download latestt drivers from Logitech website.
see if it works, and tell me how's the mouse, as am gonna buy this MX510 day after tomorrow.