HP Proliant ML350 G6 RAM connfiguration

HI there, I have a HP Proliant ML350 generation 6.  A while ago it refused to boot, so I took out the RAM.

1. I got it working again by inserting 2 x 512 RAM sticks (See photo).

2. The remaining RAM I cannot get the machine to accept.

3. Does anyone know which slots the RAM should go in, as the guidance is vague?

Thanks in advance. 

https://1drv.ms/u/s!AsxBeBCo6aUFjsoo4SkwirtiTQFsgg 

https://1drv.ms/u/s!AsxBeBCo6aUFjsoqH_pZHjjQTnIh2Q 

https://1drv.ms/u/s!AsxBeBCo6aUFjsopCHBXccvWDsYShg