My passport containing a valid visa has expired. I've obtained a new passport.
Do I need a new visa?
 -If the passport in which your visa has been endorsed has expired, the visa in the old passport still can be used, provided that you also carry a valid passport of the same nationality.
 Note: If, when canceling your old passport, the passport authority has clipped the corners of the passport, and, in so doing, has damaged the visa in any way, that visa is no longer valid and cannot be used for travel to the United States.

Does a visa guarantee that I can enter the United States?
 -A valid visa permits you to apply for admission to the United States when you arrive at the airport (or other port of entry) in the United States.
 The U.S. Customs and Border Protection (USCBP) at port of entry makes the final decision as to whether you may be admitted to the United States.
 It also decides how long you may stay in the United States.

I have a visa, do I also need a return ticket?
 -If you hold a visa of any classification, including a B-1/B-2 visa, you are not required to hold a return ticket; you may enter the United States on a one way ticket.
 All travelers should carry with them for presentation to U.S. officials, if required, evidence of funds sufficient for their visit and, with the exception of H and L visa holders, evidence that they have a residence abroad to which they intend returning at the end of their stay.
 Examples of such evidence include: traveler's checks; return tickets; copy of latest bank statement; letter from parents saying they will support you; evidence of current employment; evidence of enrollment at an academic institution.