This is a really good thread and is bound to be helpful to many others. I can remember a few similar situations with folks trying to do things like this but had no USB boot or no CD drive, so the information in here is valuable.

Thanks to those who contributed info here, and thanks to the OP especially for that last post. Very helpful!

Cheers.

I would like to add that for older laptops I would use APM instead of ACPI, because the implementation of ACPI may be buggy. Of course, you can also try other boot flags in case it is something else that is causing the problem.

The thing is I started using linux after ACPI was introduced (it was the era of slackware 10.2 and kernel 2.4.33 :P) and if i'm not mistaken that was a transition period from APM to ACPI, so i don't know much about their differences.

The thing is, in my BIOS settings screen I have seen the title saying 'ACPI BIOS 1.7'... so i guess it is acpi enabled. go figure...

Finally, i should state that I have APM enabled in my custom kernel. An interesting uncontrolled effect of that is that sometimes the laptop reboots as expected while others it completes shutting down properly and the awaits frozen, so I have to restart manually.....

using FreeDOS and USB flash drives to do a BIOS upgrade
 

Here's a good description of how to use FreeDOS to do a BIOS upgrade (mod the Sys76/LumU2-specific things).