Lost access to office on W2k PC/Installer 2755 error

[Chris]

Have a W2k Pro machine, which has Office 2000 installed
on it. All of a sudden, this machine has stopped
recognising that this is installed and now asks for the
program disk each time you go to open an Office ducoment,
to reinstall. However, this only gets to the licence key
bit then brings up an error 2755 message.

This same message also appears when trying to install
other software.

I have loaded Service pack 3, incidentally.

Any ideas?

Chris