The hotel is located at 4900 South Syracuse St.
Room keys malfunctioned with the transition to the new year.
Denver Police say they were called to the hotel as fights broke out among frustrated guests.
One 9NEWS viewer says people were getting sick in the halls, and the elevators were not working.
Denver Police say there were no serious injuries.
The lock-out ended around 3 a.m. According to Marriott, they have comped the rooms for all of the guests due to the inconvenience.
9NEWS has also heard from one person in Hawaii who is staying at a Marriott. She says their entire hotel was also locked out around the same time.
Two other Denver Marriott hotels say they did not have those problems.
(KUSA-TV © 2011 Multimedia Holdings Corporation)