Q My computer keeps telling me I have a "CMOS Checksum Error". What's wrong? What should I do?

A The CMOS (Complementary Metal-Oxide Semiconductor) error message is referring to a battery-backed chip on your motherboard that holds hardware configuration information. Some of it ù for example, the type of hard disk you have installed ù is pretty important.

This data is not something you want to lose. If you don't have a program like Norton Utilities or Nuts & Bolts that backs up the CMOS information, you need to print it out or write it down. Enter the PC setup program by pressing <Delete> or some other key (often noted on screen) early in the boot-up process ù before Windows starts loading. Go to each screen of the program and press <Print Screen> to make a printout, or write down the info.

About that error: your PC generates the error if it thinks the CMOS information has changed without your having changed it. A virus, a dying battery, or a one-time anomaly can cause this situation.

When you get this error message, you need to restore the CMOS settings. If you have Norton's or Nuts & Bolts' Rescue Disk, reboot from that emergency boot floppy and follow the prompts. If your backup is on paper, you'll have to enter your system's setup program and restore the settings manually. If you don't have a backup, research your system's configuration using printed documentation, or call the vendor.

When you've re-entered the information, save your changes and boot your PC. Make sure everything is working properly, then close Windows and turn off your computer. After a few minutes, turn it on again. If the error returns, you've got a dying battery. You'll have to open your PC, find the battery, and replace it ù or find a technician to do the job for you. If your battery is soldered on to the motherboard, you'll have to replace the motherboard, too. (Computer batteries last about five years.)

If the problem isn't the battery, update your antivirus program and run a scan. If the scan doesn't find anything, hope that the CMOS loss was a freak accident and won't happen again.