I also had some trouble running DOS on laptops newer than 2000. Most of that was due to the APM and ACPI power management, or the multiple outputs display.

On my Toshiba laptops, there was a TSR program required for running DOS (and also installing Windows). I also tried an HP laptop that would randomly switch-off because its fan was not activated without installing a driver (IDK if there was one for DOS).

Did you also test the RAM with Memtest, or check the chemical capacitors? You can never be sure with the hardware from that era.

I haven't checked the multiple display settings yet. Could be something!
What is the TSR program called? What version did you use?

I will memtest it now, thank you for the idea!

I have a second problem, the laptop randomly reboots itself. Sometimes it reboots while the BIOS is in POST mode...
It only started crashing while doing heavy file copying via LAN or USB, I am playing a 3D game and it works fine. I even looped 3DMark 99 for 2 hours without a crash.
I have no clue 🙁

edit:
Ok, now it locked up after like 20mins of "Dethkarz"

I got freaky memtest errors and build out the 256MB stick.
With the remaining 128MB everything seems to be fine 😀