Question Author
Thanks again.
The XP machine is a Fujitsu-Siemens model that we bought directly from them when they were selling via mail-order. At the time of purchase, some seven years ago, it had one 128mb SDRAM dimm installed.
About five years ago, we bought 3 DIMM modules from ebuyer and discovered soon after removing the FS installed DIMM that the system would not accept it back once it had been removed - we had the warning beep. We next tried one of the bought DIMM's and found it worked in the socket from which we had removed the pre-installed DIMM. Adding more DIMM's in the other two sockets, again stopped the PC from booting. In effect, we were now, back to square one, with a useless pre-installed 128mb DIMM and a working ebuyer DIMM in it's place.
The other two new DIMM's were installed in a HP Pavilion PC and have both worked fine ever since.
This time, after failing to get the FS machine to boot on more newly bought memory, we took the DIMM's out of the HP Pavilion and installed them in the FS machine. Now these modules were bought at the same time, had the same batch number, were the same types exactly as the FS installed memory and were known working modules.
To our horror, we discovered that the FS machine would not work on either of them.
On returning the removed DIMM's to the HP Pavilion, they worked perfectly!
It's not a socket problem, as the 32mb DIMM works in the socket from which the 128mb DIMM was removed.
Logically, the whole affair doesn't make sense. If they were from different batches or different types or even bought from different suppliers, I could accept a problem might arise.