how can remove this website address from my safari?

Hello, guys:
I am a new mac user here. happy new year!
I actually just purchased a mac this X'mas.. when I open Safari, there is this address I just can't get rid of http://gift-secure.com/?sov=24320.
I have tried to change home page, remove cookies, and run anti virus. NO luck.
And it gets worse.
If I go to facebook, Safari just shut down so fast.
Can anybody help me with this ? Thank you in advance!