Tmobile iphone unlocked question ! Please help!!!?

Tmobile iphone unlocked question ! Please help!!!?

Okay so i got an unlocked iphone 3GS 8GB.
and i connected it to my computer and it says that i need to restore and update.
so i do.
but then it tells me there has been an error .
and it goes back to a usb cord and the itunes icon on my iphone and it doesn’t want to go away
everytime i turn it off and on i goes back to the same icons.