I cant start the game help~!!

[Starcake]

i allready install half life,steam,ESF1.2version,and i found that there r a "Earth's Speacial Forces"in the THIRD PARTY GAME list,i double click the game it show the Purchase Package...i stuck at there?how to start it..do i need any ORIGINAL CD KEY or something else...plz help me thanks

 

[PRJ]

Uh if you didnt insert a legit cd key then you cant play ESF ^_^