Dell Vostro 15 Sudden Boot Failure and solution

So a colleague explained that the laptop went down suddenly while working on it. It could not be booted. 

Symptoms are the memory error LED code, caps lock is on, and no life.

Disassembly and removal of the RAM, and swapping around it appears that the DIMM slot B is not working. Both modules are functional in slot A. Something is wrong with slot B.

Inspection revealed no obvious problems. The connector was cleaned and dusted off. Some small area of the PCB looked like it had something there, right on the connector pads of slot B soldered to the PCB. It was very small and needed a microscope. With higher magnification, some particulates between 2 solder pads of slot B were seen. At first I thought this could not be it. The debris was not metallic and seemed whitish in color. After cleaning these out with a needle probe and reseating the RAM, the laptop booted without issue. Could have been metal oxides from moisture reactions with some liquid and metals. Why suddenly and definitively? No idea. 

Given the timing, speed, and low power of memory, any mismatch in data due to even a slight influence of the signal lines, will give errors. So whilst this was a memory issue, it was unusual in that the problem was on the PCB itself and not the contacts of the connector or the RAM, as is usual for troubleshooting these. 

Hopefully someone else with similar issues can solve theirs. 

T