How to Fix a BIOS ROM Checksum Error

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Basic input/output system (BIOS) is a system default utility mechanism that contains all specification details of your computer. Whenever your computer boots up (starts up), a checksum procedure is carried out by the system BIOS. A checksum procedure checks an Operating Systems' files and folders for consistency (whether corrupted or not). If the consistency checks fail, then a checksum error is displayed.

Step 1

Go to 'Start' >'Turn off your Computer' >'Restart.' Press Enter. Wait for your computer to shut down. When it starts booting up again, press 'Del/F10' key. You will be redirected to BIOS of your computer. Note different parameters listed down in your BIOS. These parameters are ideal temperature of functioning of your computer, time and date and booting sequence of different devices. Use navigation keys listed at the bottom of the BIOS window page to navigate. Press ESC and 'Y' to come out of BIOS. Your computer will start to boot up again. Let it boot and then shut it down by 'Start' > 'Turn off Computer' > 'Shut down'. Once your computer is switched off, remove all power plugs connected to it.

Step 2

Take off the outer casing of your CPU by removing the screws and sliding off the outer case to one side. Locate the CMOS cell on the motherboard of your computer (motherboard is a rectangle shaped circuitry inside the CPU). A CMOS (complimentary metal oxide Semiconductor) cell is a silver colored, coin shaped cell, resting in a socket of the motherboard. Pull it out of the socket gently.

Step 3

Put the new CMOS cell in old one's place. Replace the outer casing of your CPU. Screw the outer casing and connect all power cords that you removed earlier. Now, switch on your computer.

Step 4

Enter BIOS once again just as you did earlier. Tally the parameters that you copied. Only one i.e. the time and date would have changed. Set it right by entering the correct time and date from your keyboard. However, if any other parameter is changed, then set it correct by navigating through to it and press Enter when you reach the desired choice.

Step 5

Press ESC and then 'Y'. Your computer will start booting up. The task has been completed.

Things You'll Need

  • New CMOS cell

  • Phillip head screwdriver


Change the CMOS battery every 5 years.


Do not perform the above mentioned tasks without switching off the power.

Do not fiddle with anything inside the BIOS if you are not sure. You may end up buying a new motherboard in that case.

Make sure that you align the battery correctly i.e. positive end of battery with positive end of socket.

Make sure that the CMOS battery rests properly in the socket.

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