If this does resolve your issue, reboot the computer and determine what TSR or screen saver was causing this issue.
Older computers may not have a BIOS that is compatible with any year 2000 dates.
If your computer was manufactured before 1995, we recommended that you contact the manufacturer to determine if the motherboard's BIOS is Y2K compatible.
APM, or Advanced Power Management, can cause issues with the computer keeping time.
If the date has reset to the BIOS manufacturer date, epoch, or a default date such as 1970, 1980, or 1990 it is a good indication that the CMOS battery is failing or is already bad.
Before replacing the battery, set the date and time to the correct values in CMOS setup and save and exit the setup.
If, after saving the values, the date and time are reset when turning your computer off and on, set the values again but this time leave your computer on for 2-3 days without turning it off.
In some cases this can help enable the CMOS battery to retain its settings for longer.
Verify this is not the issue by entering CMOS setup and disabling APM or Power Management.
If this does resolve your issue consult with the motherboard manufacturer or computer manufacturer for a possible BIOS update.
Third-party utilities or programs or screen savers can cause the time to stop or decrease significantly.
If you are running Windows close all screen savers and End Task all TSRs and disable all screen savers to ensure your lost time is not being caused by this issue.