After 6 months of overstay (unlawful presence) you are barred from gaining O-1 status (or any other status) for 3 years. After 12 months of out of status (unlawful presence) you are bared for 10 years.
You should immediately contact an attorney to mitigate the damage your overstay and unlawful presence may have caused. There are waivers you can seek, even if you are subject to the 3/10 year bars. However you should not seek these without the assistance of an experienced immigration lawyer, in particular one that has handled non-immigrant waivers of inadmissibility.
Representing clients throughout the US and around the world: www.PogueImmigrationLaw.com (513) 549-4420. We cannot provide legal advice or recommendations unless you retain our law firm to represent you. No attorney/client relationship will begin until you sign a representation agreement and make a retainer payment to open a case with us. Any information found here is general in nature and should not be relied upon in individual cases.
How long overstayed? if more then 180 days, I agree with attorney Pogue.
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You will have to leave the U.S. and apply for an O visa once USCIS approved a visa petition on your behalf. You will be barred for 3 years from being granted the visa if you overstayed your admission for 180 or more days. However, the Consulate still has discretion to deny you a visa even if you leave prior to having accrued 180 days of unlawful presence. You should consult with an immigration attorney to assess your case.