Few possible reasons. Most likely is that you're rendering the "Work Area" rather than the full composition and you're work area has only 1 second of timeline contained within it. The work area is defined by the bar above your first layer and below the time/frame scale.
If that's not it then you can post a screenshot of your comp and we can see from there.
Sorry for this issue. Did you ever find a solution? Please let us know if our expert's advice helped you or if you still need help.