In the event that the BIOS is completely inaccessible due to an unknown password, but the system will still boot up, then run debug and enter the following instructions:
C:\>debug
-o 70 17
-o 71 17
Now reboot. Notice that changes to CMOS take place immediately and the old value is completely lost. That is why the CMOS RAM does not lie within the regular memory address space. It would be far too easy to corrupt, which can render a PC unbootable. Upon reboot the BIOS should complain about a checksum failure and want to reload defaults. Enter BIOS and load defaults, then autodetect the hard drives, set the boot sequence to A:, then C:, then CD-ROM, and disable virus warning. Save and Exit. Notice that this debug trick trashed all of the BIOS settings and if a particular device had been set to some obscure non-standard resource settings it may be impossible to get that device to function properly ever again since the old values were completely lost. This should only be done on systems where there is absolutely no other choice and the customer has been made aware of the potential for leaving the PC or some component in it unusable.