I just ran into this problem tonight!
I installed soundswitcher on a system i built for a friend (a program with a hotkey to switch audio from speakers to headphone on the fly without having to go into sound properties or unplug the headphones) and when i clicked restart to make sure it autostarted in windows , the system shutdown but the fan stayed on at full speed, and no display and no HDD activity. Just stayed there, like described above..
I did a hard power off, and tried to reboot, but again fan full speed and no display or HDD activity.
so i checked all cables in the back and saw the audio out 3.5mm jack halfway unplugged, so i pushed it in all the way, and powered on, and voila, she boots!
I tried to recreate the problem but was unable to get the jack to stay in the same position that i found it in..
over sensitive motherboard?
Dunno... unplug all but power cables and try shutting down , if still hangs, try again and unplug KB as well and use the power switch 1/2 second press to shutdown.. If shutsdown ok, then suspect peripheral device. USB cameras are usually a big problem, especially logitech.
system specs:
[h=1]ASRock 970A-G/3.1 AM3+/AM3 AMD 970 SATA 6Gb/s USB 3.1 USB 3.0 ATX AMD Motherboard AMD 8350 8core 4.0/4.2 GHZ[/h]8GB DDR3
3TB toshiba HDD 7200RPM
Dual boot
Win 7 ultimate x64
Win 7 ultimate x86 with video driver disabled to run Warcraft II and other ancient retro games without dosbox!