Inspiron 660, memory upgrade failed

I have 4GB of memory and would like to add another 4GB. I contacted a supplier who sent me several modules, none of which worked in combination with the existing Dell-installed module. At each attempt I first tried the existing module in slot #1 and the supplier module in slot #2. I then reversed the modules and got the same result. However the supplier's modules did work when I tried each one on its own, that is without the Dell-supplied one in place. The new supplier modules which I tried were as follows:

Attempt no        Chipset       Voltage
==========        =======       =======
     1             1Rx8          1.35v
     2             2Rx8          1.35v
     3             2Rx8          1.5v

I then removed the Dell-supplied module and installed two supplier modules of 4GB each (same spec as attempt #1) and this too didn't work. Any suggestions?

Here's a photo of the existing module: 
https://drive.google.com/open?id=1Xwstqkg0aSZKcdlHhhiHsMoEOPfNs8nj

BTW I don't understand anything about chipsets and voltages, I'm just repeating what the supplier has told me!