Q I hope you can help me with a problem computer which plays Happy Birthday to me every time the system date is 13/11/yy. It is an Intel 486DX2/66 running DOS 6.2 and Windows 3.11. When the date is 13/11/yy, just before the screen should say "Starting MS-DOS", the computer starts playing Happy Birthday and will not stop until the date is changed. I have tried three different Virus checkers (Vet, Norton Antivirus and Thunderbyte) and they all state "No Virus Found". I have substituted the hard disk with another one, but I get the same results. Could the problem possibly be in the CPU or some other part of the motherboard?

A To understand the nature of the problem, you need to understand the boot-up process. When you turn on the computer, a minimal operating system is loaded called the system BIOS. This is stored in a chip on the motherboard. This tiny operating system is capable of doing one thing only, and that is loading another operating system, such as Windows 95 or, in your case, DOS.

It does this by looking at the boot record of either a floppy disk or the hard drive. Operating systems store the information needed to boot themselves in the boot record. For this reason, the boot record is one of the places where viruses are commonly programmed to reside, so a virus could load from the boot record before the operating system loads.

However, you know that this isn't caused by something loaded on the hard drive because you replaced the hard drive. Another way to check is to see if you are getting the same problem with a clean boot floppy disk.

This suggests that the code that is playing happy birthday is residing in your computer's BIOS. You are probably wondering, how did it get there? Many computers now come with EEPROM (Electrically Erasable Programmable Read-Only Memory), more commonly referred to as Flash ROM. This can be overwritten, and motherboard manufacturers use it so that they can easily distribute BIOS updates. Flash ROM is pretty standard on current systems, and your 486 could also have Flash ROM.

Theoretically, a virus could write to a computer's Flash ROM, and there is at least one virus that does this called the CIH virus. However, the BIOSes on different motherboards are different, so a virus would have to be hardware-specific to be able to rewrite the BIOS in a meaningful way. The CIH virus merely corrupts the BIOS, making the computer unusable.

A more likely explanation is that a disgruntled employee reprogrammed the BIOS during manufacturing. Rumour has it that American Megatrends (AMI) experienced such an incident about three years ago, but I haven't been able to confirm this.

If your computer has a Flash ROM you may be able to get a BIOS update from your motherboard manufacturer's web site. If your BIOS does not use Flash ROM, you may be able to purchase a replacement BIOS chip from the manufacturer or computer reseller.