Precision T5600 - POST boot issue - Which RAM configuration

So, my T5600 suddenly stopped booting up.

Power button is solid amber and indication lights 3 & 4 are blinking.

According to the manual it relates to a RAM issue.

Any suggestions to how to find which RAM module is giving the boot issues?

Running a dual CPU configuration with 128GB RAM (8x16GB) installed.

Which RAM configurations can I run?

Help is appreciated!

Cheers