"From beyond the stars" achievement should unlock right after you gave all the pieces to Omega (mission S&F "O?" will appear once you have all of them). Just go talk to him and it'll unlock.
If it didn't indeed unlocked... well... I think you'll have to do it from the start.
Also keep in mind that you have to use NONE of the GTA cheat. If you do so, no achievement will unlocked. Just hope for you that you didn't use any. If you use any of them, you'll to use a previous saved slot where you're sure no cheat was used and restart from there.
Last edited by NoNameX03; 01-25-2014 at 10:46 PM.