I think I'm seeing similar problems with 6.1.3 on i386. In my case the system hangs hard not long after coming up and with very little activity. I've tried breaking into DDB and forcing a crash dump but either I can't get into DDB or when I do the crash dump doesn't complete. This is with the GENERIC kernel.
This same hardware successfully runs NetBSD 5.1.2, Windows-XP, FreeBSD 9.2, Kubuntu 14.04 and OpenSUSE 13.1 without any problems. I suspected a hard disk problem, but swapping out the hard drive didn't help.
