Computer time and date get reset or losing time
Computer CMOS battery failing or bad
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 the values are lost after turning the computer off and back 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.
If this does not resolve your issue, replace your CMOS battery.
Note: 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.
Issue with APM
Third-party utility or program
Third-party programs or screen savers can cause the time to stop or decrease significantly. If you are running Windows, close and disable all screen savers, and End Task all TSRs to ensure your lost time is not being caused by these programs.
If this does resolve your issue, reboot the computer and determine what TSR or screen saver was causing this issue by disabling one TSR at a time. You can also leave the screen saver disabled to eliminate that as the cause of the problem. Once the culprit has been located, see if the program has any available updates to resolve your issue.
Some computer viruses can infect a computer and cause the date and time in the operating system to be incorrect or reset to a wrong timezone. The cause is typically due to a virus interfering with operating system files that manage the date and time or causing operating system files to become corrupted.
We recommend that you run a virus scan to see if your computer is infected. If any viruses are found, remove the viruses from your computer to eliminate the infection. Change the date, time, and timezone back to the correct settings, then restart the computer.
If the date and time are incorrect again after restarting the computer or after a few days of using the computer, there may be corrupt operating system files causing the issue. Determine when the problem started to occur, then restore the operating system back to a previous date before the problem occurred the first time.
Corrupt operating system files
It is possible for operating system files to become corrupted, causing the date and time to be incorrect. Corrupt files can occur due to a virus infection, as mentioned above, or for a number of other reasons. The best option to fix corrupt operating system files is to restore the operating system back to a previous date before the problem occurred the first time. The restore process will replace the corrupt files with good files and hopefully fix the date and time issue.
Windows 95, Windows 98, or Windows ME user
When changing the year in Windows 9x or Windows ME, the time will stop until the Apply button is pressed.
When changing the month or date in Windows 9x or Windows ME, the time may decrease by 5-10 seconds.