The failure affected Russian computers on the ISS
The station's three crew and seven visiting shuttle astronauts are not at any immediate risk; the ISS has not lost all vital systems.
But it could force Nasa to extend the current shuttle mission by one day.
Engineers are unsure why the computers stopped working as a failure of this type has not occurred before.
The US space shuttle Atlantis docked with the orbiting outpost at the weekend to begin its latest mission.
Nasa's space station chief said he expected the problem to be fixed within the next few days.
"We have plenty of resources, so we have plenty of time to sort this out," said Mike Suffredini, ISS programme manager for the US space agency.
Without the Russian oxygen machine running, the space station has a 56-day supply of oxygen left. "If we are in that position, we have an option to depart," Mr Suffredini said.
Different scenarios
The station's Russian segment has a network of six computers, but on Wednesday, only two were functioning.
The computers have experienced problems before, but a system-wide re-boot usually solved the problem.
This time, the system has been unable to re-boot.
Astronauts have finished the shuttle mission's second spacewalk
The ISS is currently relying on its four gyroscopes to maintain its orientation in space, then shifting to using thrusters aboard the shuttle Atlantis when the gyroscopes are overwhelmed.
This dependency on the shuttle has caused Nasa managers to consider an extension of one day to Atlantis' 13-day mission.
If this goes ahead, the crew will have to conserve supplies - the shuttle mission has already been extended by two days in order to carry out repairs on a torn thermal blanket.
The crew of space shuttle Atlantis was originally due to spend 11 days at the ISS.
The mission was extended to 13 days in order to carry out repairs on a 10cm (4in) section of thermal blanket which peeled back as the shuttle blasted off from Cape Canaveral on Friday.
The blanket protects the shuttle from the intense heat of re-entering the atmosphere.
The shuttle docked with the space station on Sunday
The repairs could be made during a planned third spacewalk or a fourth, extra one, Nasa managers have said.
Engineers think the blanket was loosened by aerodynamic forces during lift-off, and was not hit by debris.
Damage to the shuttle Columbia in 2003 during its launch led to the vehicle's disintegration as it returned to Earth, killing all seven crew.
This was supposed to be the second shuttle mission of 2007, but a freak storm over the Florida launch site in late February caused hail damage to the shuttle and delayed the mid-March flight.
Despite the delays, managers are confident they will be able to complete the ISS before the shuttles' 2010 retirement date.
Nasa plans to fly 15 more missions to the station to deliver large components, spare parts and other supplies. In addition, one final servicing call to the Hubble Space Telescope is planned for September 2008.
Space Shuttle Atlantis approaches the International Space Station during STS-117 on June 10.



NASA has stated that they may extend the STS-117 Space Shuttle Atlantis mission by another two days to assist in the repair of 4 of the 6 computers that control the position, oxygen and water levels of the International Space Station (ISS) which failed, and have not come back on. As a result of the computer's failure, the thrusters on the station and the shuttle have been stabilizing the station's orbit.

So far, only partial restoration has been made to at least some of the computer that controls the station's position, oxygen and water, but NASA says that some of the system still needs to be cleaned up.

"They've made a lot of progress. There are some cleanup steps to do still and some investigation," said space station flight director for NASA, Holly Ridings.

Earlier NASA stated that, "Russian flight controllers will be working overnight to resolve a problem with the Russian segment computers that provide backup attitude control and orbital altitude adjustments. For now, the station’s control moment gyroscopes are handling attitude control, with the shuttle’s propulsion providing backup."

It is not known what caused the computers to fail, but Russian engineers say that it could be a problem with power supply. This type of failure has not been observed before on the space station as re-booting the computers have fixed any problems that occurred in the past, but today, that did not work.

"We have plenty of resources, so we have plenty of time to sort this out," said manager of the space station program at NASA, Mike Suffredini.

NASA officials state that there is an "option to depart" if at least one of the station's stabilizing computers cannot be fixed and the three member crew that is currently there, will have to be taken back to Earth in Atlantis. Without the computer that controls the oxygen levels, there is only 56 days of oxygen left available.

NASA had already extended the shuttle's mission by two days on June 11 to repair a tear of at least four inches in the shuttle's Thermal Protection System (TPS), which occurred during liftoff on June 8.