An end user reports that the time and date on a desktop resets after shutdown, and subsequently, the device reboots. The next day, the desktop does not load the OS and is stuck at a black screen with

Changing the motherboard is an excessive step before diagnosing and replacing a much simpler component like the CMOS battery.

Reseating motherboard power connections would not resolve issues with the CMOS battery or the system's ability to retain date/time settings.

The CMOS battery powers the Complementary Metal-Oxide-Semiconductor chip, which stores the system's BIOS settings and keeps the real-time clock (RTC) running even when the computer is shut down. When this battery fails, the date and time reset, and BIOS settings may revert or prompt for setup, leading to boot issues.

Restoring BIOS to factory default settings might temporarily resolve some configuration issues, but it will not fix a dying CMOS battery, and the settings will revert again after a shutdown.