Mouse frozen on install & won't free up

I'm new to Parallels. I'm installing the latest version of Parallels Desktop, and
assigning Bootcamp (Windows XP-Home) as my VM. The install goes ok until I'm told to continue
configuration manually. The Windows login screen appears, but I cannot free up the
mouse on the login screen (tab-arrowkey-enter doesn't work). My Mac mouse appears, but when I try to use
it, nothing happens. What can I do?