Obviously, you're able to get online, though, since you're posting here.
Yes. i'm able to get online with THIS pc, but the problem is that i wanted to install the game on another pc without internet connection.
It's weird to me that i can't do that, as others retail edition of steam games (like empire total war) can be installed completely offline
My best suggestion I can make, would be to download on a PC that has internet access, then copy the entire D:OS directory from that computer, to the one you want to play offline with. Since it doesn't require Steam to run, you should - theoretically - have no problems launching and playing. Though, you may have to install the redistributables (.Net, VC, DX) manually.