Hello,
i have a Siemens-Nixdorf PCD 4ND notebook, with 75MHz Intel DX4, 20 mb ram, trackball, and ES688 with genuine Yamaha OPL3. And WD90...something 1MB graphics card + 10.2 inch TFT screen. Great DOS machine, extremely well built, easy to disassemble (for example you can detach entire screen using 3 screws, and it doesn't use any cables - almost like in modern tablet-convertible notebooks 😜)

Unfortunately, I can't get Prehistorik 2 to work using standard system settings - it starts up, with sound and everything, the demo on the startup screen works, but when I load the first level, everything works, until I press any key. If i want to move the caveman, screen gets frozen and music continues to play. I could get the game to fully work only when I disabled cache memory in BIOS - but it has performance of 286 in such situation.
I also tried to install Orinoco Gold wifi PC card in DOS, but the system reboots when the driver gets loaded (only when the card is inside). I also have 2 additional PCD-4ND notebooks I got for parts with damaged screens, and they have the same issues.

I also have PCD-5ND, which is identical notebook, but with Pentium 1 90MHz CPU - and everything works there.

Do you know if there is a way to fix these issues? Is it a manufacturing issue, reproduced in every unit, or could that be bad caps somehow, or bad cache? (but again it would have to be broken in all of the notebooks). Maybe that could be fixed by using some kind of memory manager? (but I tried several oftware configurations, including dos 6.22 with and without himem, win 95 boot disk and Prehistorik 2 from several sources, several BIOS versions, and also several versions of Orinoco drivers - in the best case it throws a 0009 error code, and the WiFi card is activated, but the internet is not working).