Like lots of other people my computer wouldn't shutdown automatically after shutting down windows xp...I tried enabling APM, but then the computer wouldn't shutdown at all, and just restarted all the time. so I always had to manually turn off my computer when the "It is now safe to turn off your computer" screen came up.
Well I fixed this problem, and came across the solution, for me accidently. I went to Device Manager, then to View then Show Hidden Devices, then you look on the list for NT Apm/Legacy Support. Under that is NT Apm/Legacy Interface Node. I found that this driver was disabled. Why, I'm not too sure, but I enabled it and now when I shut down windows, my computer turns off automatically. I went into power management and the APM was also activated/enabled....It must do this when you enable the driver.
Hope this is of help to anyone.