Nothing useful back from the mobo manufacturer yet, but I have managed to find something out by examining the output from dmesg for booting with the HDMI cable in compared to booting with the cable out.
With the cable in (i.e. the cause of the problem), dmesg repeatedly reports:
NVRM: RmInitAdapter failed! (0x31:0xffffffff:1004)
NVRM: rm_init_adapter(0) failed
but when the cable is mometarily out, the kernel module loads successfully:
NVRM: loading NVIDIA UNIX x86_64 Kernel Module 169.07 Thu Dec 13 18:34:01 PST 2007
Unfortunately, I'm no hardware guru but I believe this may have something to do with IRQs.
If you type:
do you get error messages similar to mine? Or is everything rosy..?
Do let me know if you get anywhere. Unplugging the HDMI lead is currently the fly in my 42" of ointment...