my steam was hijacked to, but i got it back today
go to steam website and make a steam support account and klick ''ask a question''
and choose PC platform and hijacked accounts.
its gonna be hard without a picture of your cd key
play with zero gear demo , show them it still works,or tahe your cd back to store(with receit) and tell them the game has a problem(has already used cdkey, doesnt install properly,damaged cd etc.) and ask a new copy.Big stores dont usually excange copys but its worth a try.I got two copies in the price of on : P