Tried what I think is a good number of permutations of cheat codes, including failsafe, expert and debug as well as the pci, acpi and apic options on/off etc. I've also tried changing the BIOS settings in a number of areas.

Every live CD I've tried (including OpenBSD!) has failed just after the kernel loads.

I'll keep trying but am thinking I might need to find a new mobo.