What is CMOS?
Complementary metal-oxide semiconductor, or CMOS, typically refers to a battery-powered memory chip in your computer that stores startup information. Your computer's basic input/output system (BIOS) uses this information when starting your computer.
CMOS-related error messages could be caused by a faulty or discharged battery. The battery can become discharged if your computer has been turned off for a very long time. To resolve CMOS-related errors, check the information that came with your computer or contact your computer manufacturer. Because your CMOS settings are specific to your computer's hardware, Microsoft can't provide specific instructions for changing them.