Medieval Total War is not installing!

[LegendKiller45]

I have all the systems requirements, the game has worked on my p.c before.
the disc is fine, I even had it cleaned.
It loads up to 99% when installing (even accepts both discs that are needed for installation process) then a message comes up saying:

setup has detected errors in installation process


I also had a problem which said:

Please close unInstallShield and restart setup
Error 432.

I have no idea what I did but it went away and the game started installing but it still gets to 99% then a minute later when its meant to be fully installed a message comes up saying theres errors.

How do I find out what these errors are and more importantly how do I resolve the problem so I can play the game?

Please help, I would be ever so grateful!