acpi_power_off doesn't

Hi folks,

Sometimes acpi_power_off doesn't switch off my PC. If I boot and press the power button again as soon as it is up, then it shuts down as expected. But if I login, let it run for some time, logout, and press the power button, then it walks through the runlevel 0 scripts as before, finally it says

acpi_power_off called.

and keeps on running. The PC does _not_ go off.

Kernel is 2.6.16.5, Pentium M 2GHz, Aopen MZ915-M.

Any idea?

This PC is supposed to startup and shutdown without watching, so any help would be highly appreciated.

Regards

Harri