My computer detects that I have 12 GB of RAM, but says only 3.95 GB is useable... I have both sets of RAM (2 x 8 GB and 2 x 2 GB) in the correct color slots (the pairs are in the color pairs). Any ideas?
also if you have a non pined CPU like the Threadripper or intel CPUs it could be as easy as the CPU is not seated properly. so it can only use 1 channel of the ram ... like in this case the 2x2 set.. or just 1 stick... its pretty common if you just built the PC.
Remove the CPU and put it back in.. make sure it is aligned properly. (and like the previous person said.. what OS.. and other specs would be nice too. if you are on a 32bit OS that is the max you can use.