This is not a virus.
There is a a large set of trojanized AMI BIOS chips going around which halt the machine during boot-up on the 13th of November and play 'Happy Birthday' from the PC-speaker until you press a key.
The BIOS version is "M82C498 Evaluation BIOS v1.55", dated 04/04/93.
Do note that it's not a virus - it will not replicate anywhere from an affected machine.
If you have this problem, contact your hardware vendor for a BIOS replacement.
[Analysis: Mikko Hypponen, F-Secure]