If you failed to maintain lawful F-1 status (enrolled part time without authorization, worked without authorization, failed to renew I-20, etc.), you may apply for reinstatement to lawful status. Application for reinstatement procedures are as follows:
This application package is mailed to the USCIS Office in Vermont for adjudication. If an immigration officer reinstates you, you are again under lawful F-1 status. If not, you will be given a certain amount of time to leave the United States.
If you are denied reinstatement in the United States, you can obtain a new I-20, travel outside the United States, apply for a student visa, if necessary, and reenter in legal F-1 status. If this is your situation, please make sure to meet with the International Student Advisor.