2006 Hummer H3

2006 Hummer H3 Four Wheel Drive Automatic

Yesterday the DOORS sign appeared on my dash. I understand this means that a door is ajar, however, I opened and shut all my doors several times and that did not seem to work. It locks fine from the outside, but will not remained locked from the inside when it is turned on, and constantly dings at me like a door is open. Any ideas?

Thanks,
Lisa