The following is information regarding how to apply for a new F-1 or J-1 visa at a U.S. Consulate abroad.
Has the U.S. visa stamp inside your passport expired? If it is still valid, is it for multiple entry, or has the entry been used up? Finally, is the category for which the visa was issued the status your currently hold (for example, if your visa is F-2, are you currently in F-2 status or did that status change after you entered the United States ).
Any student traveling outside the United States whose U.S. visa has expired or changed status must apply for a new visa at a U.S. visa issuing post abroad before returning to the U.S. In most cases, the visa application will be filed in your home country. Appointments are now required for virtually all non-immigrant visa applications, even at U.S. embassies and consulates located in countries that didn’t previously require appointments. This has resulted in significant delays at some U.S. visa issuing posts abroad, especially during summer.
It’s important to note that the summer vacation period is an extremely busy time at visa issuing posts due to the large numbers of travelers and reduced staff who may be taking vacation. Also, in the event of any protest, threats, or terrorist attacks that are judged to be threatening to U.S. embassy or consulate personnel, government officials at those posts may temporarily close or alter their operational hours.
The State Department has also prepared two information sheets about student visas on its web site which may be useful to you as an international student. They may be obtained at: http://travel.state.gov/whatconsulslookfor.html or http://travel.state.gov/foreign_student_visas_handout.html