shutdown -r hangs

[Paul Cartwright <ale@pcartwright.com>]

I have had this issue for a long time, never resolved it. If I type:
shutdown now
the machine turns off

if I type shutdown -r now
it starts to shut down, and then it sits with these last messages on the 
screen:
[4426.174309] ACPI:PCI interrupt for device 0000:00:19.0 disabled
[4426.189849] Restarting system. 
[4426.189892] machine restart

and it sits there. 

when I hold the power button, turn it off & back on, the syslog shows this:

Nov 26 09:21:27 paulandcilla kernel: Kernel logging (proc) stopped.
Nov 26 09:21:27 paulandcilla kernel: Kernel log daemon terminating.
Nov 26 09:21:28 paulandcilla exiting on signal 15
Nov 26 09:24:35 paulandcilla syslogd 1.5.0#5: restart.
Nov 26 09:24:35 paulandcilla kernel: klogd 1.5.0#5, log source = /proc/kmsg 
started.

/var/log/messages has this:
.
Nov 26 09:21:12 paulandcilla shutdown[10505]: shutting down for system reboot
Nov 26 09:21:26 paulandcilla pcscd: pcscdaemon.c:563:signal_trap() Preparing 
for suicide
Nov 26 09:21:27 paulandcilla pcscd: readerfactory.c:1348:RFCleanupReaders() 
entering cleaning function
Nov 26 09:21:27 paulandcilla pcscd: pcscdaemon.c:523:at_exit() 
cleaning /var/run/pcscd
Nov 26 09:21:27 paulandcilla kernel: Kernel logging (proc) stopped.
Nov 26 09:21:27 paulandcilla kernel: Kernel log daemon terminating.
Nov 26 09:21:28 paulandcilla exiting on signal 15
Nov 26 09:24:35 paulandcilla syslogd 1.5.0#5: restart.
Nov 26 09:24:35 paulandcilla kernel: klogd 1.5.0#5, log source = /proc/kmsg 
started.

why won't it reboot, or what can I look at?
-- 
Paul Cartwright
Registered Linux user # 367800
Registered Ubuntu User #12459