I have a Supermicro P8SC8 motherboard that won't poweroff with ACPI using the 2.4 kernel series. I have testing it with 2.4.25, 2.4.27, 2.4.28 and 2.4.29-pre2. In all cases, the system enters acpi_enter_sleep_state after which, the keyboard leds flash once and the screen goes blank. The system remains in this state with the power still on. If I try to reboot the system via the reset switch, the machine never POSTS. I have to remove and re-insert the power cord to boot the system again.
With 2.6.9, the machine powers off as expected. Can anyone offer any advice on how to debug this problem?