The Y2K (Year 2000) problem existed because most dates in computers were programmed to automatically assume the date began with "19" as in "1977" and "1988." But when the date was to turn from December 31, 1999 to January 1, 2000, it was prophesied that computers would be so confused that they would shut down completely.
Considering how much of our everyday lives were run by computers by the end of 1999, the new year was expected to bring serious computer repercussions. Some doomsayers warned that the Y2K bug was going to end civilization as we know it.
Other people worried more specifically about banks, traffic lights, the power grid, and airports -- all of which were run by computers. Even microwaves and televisions were predicted to be affected by the Y2K bug. As computer programmers madly dashed to update computers with new information, many in the public prepared themselves by storing extra cash and food supplies.
However, when the date changed to January 1, 2000, very little actually happened. With so much preparation and updated programming done before the change of date, the catastrophe was quelled and only a few, relatively minor millennium bug problems occurred.