Help! Microsoft Office Ultimate 2007 setup error

Help! I have recently bought a new notebook computer (laptop) which came with
a trial version of Office 2007. In the meantime while I was using the trial I
purchased the above suite thinking it would be best for what I needed (I'm a
university student). When the trial ran out, I tried to enter the product key
for my bought copy but that didn't work so I deleted the trial completely off
the system and then tried to load my bought version. However when I tried to
load it I got the following error message - "Setup cannot continue because a
required file is either corrupted or not available. Run setup again from the
original source disk or download location."
Can anyone help me please?
Kim