I have the same problem as well.

Mine used to shutdown automatically before I upgraded to kernel 2.6. I used to use 2.4 and it worked ok.

I think I know a little bit of why it does this.

I've noticed that during bootup it gives an ACPI related message about my BIOS being "too old". I've done some reading up on this. Here is appearantly what is going on.

Back when I was using kernel 2.4 my system was probably utilizing APM instead of ACPI. There is appearantly some advantage to ACPI (I'm not sure what they are because I haven't had the time to do some serious research on the tons of info on ACPI out there. But suffice it to say that ACPI goes beyond just power management and has to do with configuration of some PCI devices etc.). Anyway, I believe alot of stock kernels come compiled by default to disable ACPI if your bios dates after a fairly more recent date (can't remember the exact date) just to play things safe.

There is a way to override this though. I've read of how to do it before, but can't remember exactly. I do believe there is actually a few different ways. One way that I remember was to force ACPI support through a kernel parameter on bootup.

The problem for me is that I can't seem to find any information to determine what the ramification of forcing ACPI support are. For example, how can one determine if it is or isn't safe when their BIOS is "too old"? Would it be a better idea to somehow enable APM instead for one of these "too old" BIOS?

Sorry I can't be of more help. But I'm guessing that those of you who are having the issue of where the computer used to shut down automatically, but now doesn't, have probably upgraded your kernel up to 2.6 by whatever means (upgraded distribution etc etc.) like in my case.

I think that probably the more important thing is finding out what the ramifications, of why ACPI is being disabled, are. And then take things from there be it to figure out how to reenable APM or force ACPI to be enabled if it can be determined that it will not create any less than obvious issues.

for me what worked was adding the line append="apm=power-off" to lilo

thank you for your answers but i still wasn't able to solve the problem, nothing worked for me.

Just make sure the obvious isn't being missed, try

poweroff

or

halt -p