CMOS Checksum Bad or CMOS Date/Time Not Set
This issue is caused when the CMOS values are incorrect. This issue can occur because of any of the below possibilities.
* Bad or old CMOS battery.
* BIOS update.
1. Disconnecting power from computer without shutting down computer.
2. Attempt to reboot the computer. If error still occurs after rebooting the computer enter CMOS setup and check all values, this includes verifying the time and date are correct. Once everything has been verified and/or changed make sure you save and exit CMOS setup.
3. If you have a Phoenix BIOS and have an option for 'Reset Configuration Data', set this value to 'Yes' and save and exit the CMOS.
4. If the computer was had the power disconnected while it was still running it is possible this could cause the CMOS to become corrupt. Ensure that the computer is ready to be shut off before turning off the computer. If you have a laptop computer ensure that the battery is charged before disconnecting the power connection.
5. If the CMOS values have become corrupted entering the values in CMOS setup and saving and exiting CMOS should resolve your issues.
If this issue continues to occur after you turn off your computer off it is possible that the CMOS battery may be failing or already bad. Before considering replacing the CMOS battery try leaving your computer on for several days.
If you performed workaround 1 and the error occurs again after a complete power down (i..e. removing the power cord), the CMOS battery is likely bad. Most systems use a small coin style lithium battery. These often last 3-6 years, but at some point run out of juice and need to be replaced. For desktops, your system manual or motherboard manual should specify the type of battery and location on the motherboard. For laptops, it is often very difficult to access and may require a professional to replace it. To replace the battery on a desktop system:
1. Turn off the system and remove the power plug.
2. Remove the case or side panel to access the motherboard.
3. Look for a round silver coin cell, typically in a black holder.
4. Remove the battery while noting which way the battery is located. You may need a small flat screwdriver to release the side clip.
5. Install the replacement battery with the same battery type, being careful to insert it in the same direction as the removed battery (or using the polarity marked on the holder or manual).
6. Reassemble the case and power.
7. Turn on the power. You will get the CMOS Checksum Bad error once more, but it should be the last time. Go into the BIOS setup and set the date and time, and any other options you prefer.