2008 macbook won't take more than 3gb ram

Question

So I bought some ddr2 ram for my MacBook and when I installed it the computer black screened with no chime. So I tested each stick with the same result I even reset the SMC memory to see if that fixed it and nothing. However when I installed just one of the 2GB sticks with one of the 1GB sticks it already had, the computer boot fine and when I checked the system profiler it noticed the ram perfectly fine.

Answer 1

Some models of MacBook required a firmware update; and of those
(unknown percentage of models or their specifics) some could only
see a greater upgrade in RAM or to use a later OS X, once done.
Perhaps the RAM you are trying to use is not correct spec to the Mac.
Or maybe one of the chips has an issue whereby it doesn't connect,
so a clean pencil eraser could be carefully used to wipe fingerprints or
dust off the connectors. And never handle RAM by those contacts.
Several early MacBooks had a ceiling of 3GB, though two 2-GB
chips could be installed if that is what you happen to get; but that
did not necessarily equate to a noticeable improvement in function.
However the Early 2008 MacBook 13-inch model is said to support
up to 6GB RAM: one 2-GB chip & one 4-GB chip; of correct spec.
Both the Early 2008 and Late 2008 (white/black) models can use:
Maximum Memory    6.0 GB (Actual) 4.0 GB (Apple)
Memory Slots    2 - 200-pin PC2-5300 (667MHz) DDR2 SO-DIMM
according to http://mactracker.ca specification database
Also, if the MacBook is of the Aluminum unibody version, that uses
a different specification of RAM, and also has higher ceiling total...
{If the RAM is from some 'poor quality' source, there is a fair chance
it is not good or stable in the Mac. There is a noticeable difference.}
So that may be the problem... hard to say without more information.
Good luck & happy computing!