Installing Office 2011 breaks my Outlook settings

Hi everybody!

My first post on here so please be gentle, especially as this might get a bit long for a first post. 

I've got an odd problem with the installation of Office 2011 on my Mac Mini. It goes as follows:

Mac Mini - i5, late 2012, Yosemite fully updated.

I have a licensed copy of Outlook 2011 which is provided by the company I use for my Exchange mailbox (Fasthosts in the UK, running on Exchange 2013). There is no license key for that product as it is supposedly "locked" for use with my email account only. I installed it on my clean install of Yosemite and it auto-connected just fine and synchronised with my Exchange email account fully without problem.

Once that was working, I then installed Office 2011 Home & Student to get Word, Excel and Powerpoint. Unfortunately, there is also an unwanted and un-advertised "trial' version of Outlook 2011 included on the DVD which seems to mess-up the Exchange Server connection settings. I guess it's replacing some essential info somewhere, but there's no option NOT to install the Outlook trial and I can't reconfigure Outlook at all to make it work. (Tried deleting account and recreating, but it didn't help).

Where Outlook used to connect, now I get a prompt saying:

The server for account "W*******m" returned the error "Logon failure: unknown user name or bad password." Your username/password or security settings may be incorrect. Would you like to try re-entering your password?

Now I know that my username & password are correct (they worked before) so I guess the unwanted repeat installation of Outlook is messing up security somehow.

As an alternative approach, I deleted Office thoroughly and tried installing Office first and then my licensed copy of Outlook, but I just get the message that I need to upgrade the Office package to make Outlook work.  I've since repeated the full deletion of Office and reinstalled Outlook 2011 to my exchange account successfully, only to find that installing Office messes things up again.

I've gone round in circles trying different things and still end up with a non-working Outlook.

Does anybody have a clue how I might either fix (or identify) the info that is being trashed.
or
Any idea how I can tweak the installation of Office 2011 to forget about installing the unwanted trial version of Outlook?

Many thanks for reading all of that!
Best regards,
Paul.