[AccessD] Access 2010 Indexes

I haven't used A2010 that much so forgive me if this is a daft question, but
when I'm in table design and have the index window up the index properties at
the bottom are greyed out and I can't change them. Why? I see my individual
indexes and can select any of them. I can add and delete indexes so it's not as
if the anything's locked or read-only and yet I can't, say, change one to
Unique. All that happens when I hover on or click the 3 properties at the bottom
(Primary, Unique, Ignore Nulls) is that I get an explanation of that property
overlaying where I should see the options to set Yes or No. For example, I try
to click on or next to 'Primary' and I have the words "If Yes, this index is the
Primary key". What I don't have is the Yes/No selections. I can't even see what
each property is currently set at. Can anyone tell me how to resolve this?
 
Cheers
 
Andy