Software install MS Office disc on iMac

I have upgraded to a 27" iMac from a 20" using Migration Assistant but the Office will not transfer so I am needing to re-install on the 20". I had erased the HD and re-insallted OS X prior to giving my brother the computer.

The MS Office disk won't show on the 20" and gets ejected quickly. But other discs are OK and the Office install disc is OK on the 27"

What I am I doing wring please?

Stuart

I have 10.10.3 on both machines.