The extent of the problems that may occur if a computer's clocks fail to recognize the year 2000 are hard to quantify.
Predictions range from the relatively minor to the apocalyptic.
But, if organizations fail to address the Millennium bug, products and services that rely on computers to function efficiently will undoubtedly be at risk. When the computer is off, a battery keeps the Real Time Clock running just as a battery can be used to keep a watch running. That value is set at 19 for the current century. When the century changes, this value will remain at 19. If the BIOS, Operating Systems, and any programs that use the RTC to get the date do not allow for this, they will give false information in the 21st century, wreaking havoc in many different ways.