Hi,

You left out a lot of detail, like what operating system you are using, but
considering that you are in a NT newsgroup, we'll assume NT4.0 for the purposes
of my answer:

This question is constantly asked - the frequency of people encountering this
particular problem has skyrocketed in the last couple of years because of the
all the Virus/Worm scares and everyone finally deciding to do something about
plugging the multitude of security holes left in Microsoft OSes  (NT 4.0 included)

To answer - by any chance did you have a copy of Microsoft Intellimouse prior to
V3.2 installed on the machine ?  There is known issue of the 'POST SP6a Security
Rollup (SRP) Q299444' breaking the mouse and keyboard when it is installed under
these conditions.

Have a look at Microsoft Knowledgebase Article 305462 - Title: "Mouse and
Keyboard Stop Working After You Install the Windows NT 4.0 Security Rollup
Package". I think it will address your particular situation. They offer several
possible fixes for the problem, depending on what type of file system your boot
partition is. (ie: the one that has the /WINNT folder on it)

I managed to cure my particular problem by remote logging in over our LAN and
manually replacing the effected files - fortunately they weren't in use because
they had failed to start. Once I got a working keyboard and mouse, I properly
removed Intellimouse V2.0 using Add/Remove programmes and replaced it with a
later version (V3.2 or later is ok)

The particular knowledgebase article and scenario may not be applicable in your
case - we'll need more detail to be able to give a more helpful answer.

Regardless, the failure mechanism appears to be the same, and undoubtedly will
have a similar root cause - ie: at some stage your application of later patches
(SP etc) has made one of the keyboard/mouse drivers incompatible with the
system, rendering them impossible to start.  I presume the mouse and keyboard
are PS2 type? If you leave the system alone for 60 seconds or so once you get to
the login screen (and dead keyboard) do you get any 'Service Control' warnings
about 1 or more services/devices failed to start ?

It may take some detective work on your part, but particularly if you can manage
remote access to the machine via a LAN, or access to the files of the 'broken'
installation via a parallel install of NT4 (or other means) all is not lost.

If you do want to attempt a parallel install, and are unsure of what you are
doing, please ask here, or have a search of the list of Knowledgebase articles
on this page:

http://nt4ref.zcm.com.au/kb.htm

looking for the words 'parallel' and 'install'.

WARNING: Repairs of this nature can be tricky, and you need to be sure of what
you are doing, lest you take a bad situation and reduce it to unrecoverable :-(
If in doubt, ask more questions, or seek skilled guidance and support.

Calvin.