A big-ish machine, cannot boot

I have a large-ish marchine, a Fujitsu TX300 S6 with 2x6-core + HTT CPUs
and 24 GB RAM, configured as a demo machine with lots of interesting
hardware.

Unfortunately, the kernel hangs on boot. The loader finishes, the twirly
starts spinning but then hangs. Enabling verbose booting results in
nothing new - no kernel messages at all.

Any ideas?