United Airlines says its computer systems are back up and working Saturday morning after going down for more than five hours overnight.
Thousands of United passengers at Chicago's O'Hare and airports across the country have been affected. Many were still trying to get to their destinations Saturday.
The problems began Friday night just after 7 p.m. By 1 a.m. Saturday, United announced on its Twitter page its systems were running again.
In addition to departures, the computer outage also affected airport processing and reservations.
The Federal Aviation Administration (FAA) says because of the glitch, United passengers could not check in for their flights.
For many passengers at O'Hare, the experience was a nightmare.
"Well, we've been here for quite a while and they kept us hanging on and hanging on, and they finally let us know about 20 minutes ago that they're cancelling our flight. They were letting flights out to the United States but none that went to Canada, none that were international," passenger Louise Mackey said overnight.
United Airlines had not announced later Saturday morning what caused the computer problems or how many flights or passengers were affected. They also don't know when they will be back operating on schedule.