Usually for two stucks it goes into A2 & B2.
Or try A1 & B1.
The RAM needs to be identical sticks though from the same manufacturer to work properly.
Reset your BIOS in case any settings have been altered causing problems.
Try each stick of RAM
individually to check they both work but observe your motherboard's configuration for using 1 stick at a time i.e. the correct slot.
Run Windows Memory Test -
'
To launch the Windows Memory Diagnostic tool, open the Start menu, type “Windows Memory Diagnostic”, and press Enter.
You can also press Windows Key + R, type “mdsched.exe” into the Run dialog that appears, and press Enter.'
If all of the above steps are ok then return the second stick of RAM that causes the BSOD with both sticks in place as faulty to your supplier.
Andy