50 % of time, on reboot, Windows cannot control the A20 line [Memory] and loses Himem.sys file. Booting in A-Drive and restoring Himem.sys does not correct the problem in all cases. Allowing the CPU [Pentium II (266 or 333) to cool, usually correctsthe problem. Adding additional memory has never corrrected the problem. Changing CPU’s has never corrected the problem. There seems to be no tech manuals from either IBM or Intel for this antique computer [IBM Aptiva 2140-L61]. Could there be a jumper on the board that needs to be changed for the new memory, or new CPU? I found by freezing the 333, then the 266 and changing them out when one gets overheated seems to fix the problem temporarily, but still needs a full setup on each new boot. Also the 3-pin power cord for the CPU fan on the 333 has nowhere to plug into [Suggestion]. And the fan for the box has a two prong plug behind the CPU that no longer operates. [Suggestion]. To replace what is already built into this motherboard would take three computers.
Dr. Palmer