Steam vs Disc Installation issues

 Morning all,

 Having some trouble installing ME2 on a PC I inherited from a friend. I played through ME2 several times on my old PC (hard copy), he also played through it on the machine which I now own, but using Steam.

 I uninstalled his version of ME2 from the PC, but when I insert my disc to install the game it offers 'Play' rather than 'Install', and 'Play' opens Steam and directs me to buy the game again. I can't get the disc to give me the Install option. Any ideas on what I should do?