As opusman said, what you said doesn't make sense.
If you where issued a Visa by going into an embassy / consulate and had an interview, you must have left the US by the date of expiry of the Visa which they issued. You would also need to be careful not to do something which is outside the scope of your Visa (eg work if on tourist visa).
However what I think you have been issued is called an ESTA. That is issued by logging onto the DHS website, answering a few questions and paying your US$10. They are valid for 2 years, but only let you board the aircraft in to travel to the US. They are not a Visa (as they do not guarantee entry, a Visa will guarantee entry provided border officer thinks you are there for the genuine reason as stated by your Visa), and your entry rights will be determine at the border by the CBP officer. If determined that you can stay (unless you've lied or have copies of your resume with you, chances are they will let you stay) they will stamp your passport and that date is the date which you can stay in the US until, they will also write in a code underneath stating the purpose (WT = Tourist aka no working, WB = Business aka you can work provided you are employed by a foreign entity). You can not travel to the US on an expired ESTA, but you can stay in the US on an expired ESTA provided you leave before the date stamped in your passport.