How to Reset a Laptop CMOS

By Shoaib Khan

A laptop's CMOS is a small semiconductor chip that stores instructions required to power up the computer's hardware components when starting up the system. The hardware configuration information, along with the system's date and time, are stored as CMOS settings, also known as BIOS (basic input output settings.) CMOS, an acronym for "complementary metal oxide semiconductor," is a battery-powered unit that can be reset to clear all its information, including any passwords set for the BIOS. The CMOS may be reset in several different ways, depending on the model and manufacturer of the laptop.

Changing Jumper Setting to Clear

Step 1

Power up the laptop and immediately and repeatedly begin tapping the "Ins" key immediately. Some laptop manufacturers allow the CMOS settings to be cleared by pressing the "Ins" or "Del" key repeatedly during startup. Try with the "Ins" key first and then the "Del" key, or proceed to the next Step.

Step 2

Turn off the computer and unplug its power cord. Never dismantle electronic components with a live power source. Turn over the laptop and remove the main battery by undoing its latch under the laptop.

Step 3

Access the laptop's motherboard. You may clear your laptop's CMOS settings by changing the CMOS jumper setting on the motherboard to a 'clear' position. Refer to your product documentation for specific instructions on locating and changing CMOS jumper settings on the system motherboard.

Step 4

Remove components such as the hard disk drive, wireless card and RAM modules from the laptop, following manufacturer recommended procedures. Open the casing and locate the CMOS jumper in the motherboard. Detach the jumper and put it in its 'clear' position. This will clear the BIOS or CMOS settings.

Step 5

Reassemble the computer, insert the battery and turn it on. Put in new values for BIOS settings, such as date, time and password, when you see the "CMOS checksum error" message, as the computer boots for the first time after resetting CMOS. Press "F1" to load BIOS settings and load default values.

Draining CMOS Battery

Step 1

Turn off the computer, unplug the power cord and remove its battery pack from under the device. You will reset your laptop's CMOS settings by draining the CMOS battery.

Step 2

Locate the CMOS battery in the system motherboard. Refer to your documentation for instructions on accessing and replacing the CMOS battery. You may or may not have to disassemble the entire unit, depending on make and model of the computer.

Step 3

Remove the CMOS battery, a circular flat component, much like a watch battery. Raise the battery from its chamber by using a flat-tipped implement as a lever. Carefully hold the battery with two fingers and remove it.

Step 4

Insert the battery after 15 hours. This will clear all information stored in the laptop's CMOS. Fit the main battery back into its appropriate slot and reassemble the computer. Power up the laptop and apply new settings by pressing "F1" when the "CMOS checksum error" is displayed.

Tips & Warnings

  • One reason to reset CMOS settings is to remove a BIOS password. If you want to reset the CMOS to bypass a password, try using software to crack the password before attempting to dismantle the computer.
  • Do not take your laptop apart if it is still under warranty. This will void the manufacturer's contract. Follow instructions to dismantle your laptop. You may damage the system if you do not refer to the manual.
  • Take precautions to avoid ESD (Electrostatic Discharge) before opening your laptop. Use an antistatic wristband or pad to prevent ESD from damaging your computer.