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Error: CMOS Checksum Bad

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This document pertains to all HP and Compaq Desktop Computers.
One of the following error messages appears when starting the computer:
  • BIOS ROM checksum error
  • System CMOS checksum bad - default configuration used
    Press <F1> to resume, <F2> to Setup
  • CMOS Checksum Bad
    Press F2 to Run SETUP
    Press F1 to load default values and continue
  • CMOS Checksum Error - Default loaded
The error that appears depends on the type of BIOS used. Any of these error conditions indicate that a Basic Input/Output System (BIOS) test failed.
There are two main reasons why a BIOS test fails:
  • The battery on the motherboard has lost its ability to supply power. The system time and date are also affected by a bad battery.
  • The BIOS was updated "incorrectly". This can happen if power is lost while updating the BIOS, or when the BIOS is updated with an update that was not downloaded from HP, or when a certain virus or malicious program modifies the BIOS data.
To resolve the error, use one of the following sections.
Click the applicable BIOS version or the accompanying plus (+) sign to expand the information.
  1. Turn off the computer and wait five seconds.
  2. Turn on the computer.
  3. When the first screen displays, do one of the following:
    • Immediately press the F10 key if your computer was built in 2006 or later (came with Vista or Windows 7). Press the key once every second until a BIOS Setup utility screen opens.
    • Immediately press the F1 key if your computer was built before 2006 (XP or earlier). Press the key once every second until a BIOS Setup utility screen opens.
      NOTE:On some Compaq Presario computers (before 2002), press the F10 key at the logo screen.
  4. Press F5 to restore the BIOS defaults.
    NOTE:If an error occurs or the computer locks up at this point, the default BIOS information has become corrupted. The computer requires service or a new motherboard.
  5. Press F10 to save the values and exit. Press Y to confirm before exiting.
  6. Restart the computer to see if the error continues.
    If the error no longer appears, you are done.
    If the error appears, continue using these steps.
  7. After replacing the battery, restart the computer to see if the error continues.
    If the error no longer appears, wait until Windows opens and set the date and time to current settings.
    If the error still appears, the default BIOS information has become corrupted. The computer requires service or a new motherboard.
  1. Turn off the computer and wait five seconds.
  2. Turn on the computer.
  3. When the first screen displays, do one of the following:
    • Immediately press the F10 key repeatedly, about once every second, until the Computer Setup program opens.
    • Immediately press the Escape key repeatedly, about once every second, until the Startup menu opens. Then press F10 to open the Computer Setup program.
  4. In the BIOS Setup utility, select the File tab.
  5. Select Apply Defaults and Exit .
    Figure 1: Setting the defaults
    Setting the defaults
    The computer restarts.
    If the error no longer appears, you are done.
    If the error appears, continue using these steps.
  6. After replacing the battery, restart the computer to see if the error continues.
    If the error no longer appears, wait until Windows opens and set the date and time to current settings.
    If the error still appears, the default BIOS information has become corrupted. The computer requires service or a new motherboard.

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