Dead mouse.

> If, for instance, the mouse goes down again, what should I do, being
> able to use only the keyboard? Or is that too broad a question?

The problem is the mice are different enough that they need different
drivers. If I were to do it manually, I would get to a console
(ctrl-alt-F2), assuming you're booting straight into X. Log in and you
need to edit the file /etc/X11/XF86Config (there may be a -4 at the end
of the name) and change the mouse driver. There is a line that looks like:

Driver "mouse"
Option "Protocol" "IMPS/2"

Where you would need to change the protocol to what your new mouse uses.
 I don't remember what the options are off hand, man XF86Config or a
google search should tell you.

I'm surprised Mandrake doesn't autodetect this though. Can someone tell
us how to make Mandrake re-configure X? <something>drake?

[Religion]
I always hear how Debian's installer is horrible because it doesn't
autodetect anything and makes you know what your hardware is. I always
assumed Mandrake has this covered. Are my few experiences with Mandrake
just been unlucky? Or is that I only see other peoples Mandrake boxes
when the autodectection fails? :-)
[/Religion]

-- 
Steven Kurylo