Chassis Intrusion is implemented as a feature within the chipset.It is a latch circuit. That is, when a short occurs across the pins of the INTRL header, the circuit is latched and remains latched until cleared. There is no way to clear the latch without going into BIOS Setup or using a tool.
As Al indicated, you use the F2 key to enter BIOS Setup. If, from there, you are unable to clear the latch, you can try doing so from the BIOS Maintenance Mode settings. Power off the machine, move the yellow jumper (or perhaps that's tan, there are different interpretations of that color and it (literally) fades over the years) from pins 1-2 to pins 2-3. When you then power on, it should automatically come up in BIOS Maintenance Mode. From here, you should be able to clear the latch and also clear the unknown password. When you are done, power off and restore the jumper to pins 1-2.
Now, I have seen cases where something fails and the latch will not clear from BIOS. I created a tool (a long time ago) that I could send you that you could use to try and clear this up. It is a 16-bit DOS tool, so you would need to boot MSDOS (or PCDOS or FreeDOS) from a floppy or USB flash drive and then run the tool. Let me know if you need me to send you this tool...
Hope this helps,
...S
P.S. If you are responding to say you need the tool, don't include your email address in the response (unless you really want SPAM from all over the world). I can communicate with you using the Community's Private Messaging capability.
