Oddest problem I have ever seen

[MikeyLSU]

OK, so I helped my brother build a computer and it woudln't start up. We each have 2 GB of DDR2 RAM and basically have the same computer.

Specs don't matter...but the problem.

So we have 4 sticks between us.

His computer power would come on then turn off and on in about 3 second increments by itself when turned on. We ended up finding out that 1 of the sticks was bad and by taking it out the computer booted up and worked.

Great.

Then we decided to test out his RAM on my computer just to make sure that was the problem.

To simplify the explanation lets say we have 4 sticks of RAM, 3 good sticks(G) and 1 bad stick(B).

the computer will work in the following scenerios:
G
GG
GGG
GGB

but will not work on these
B
BG
GGBG

order does not matter, but I can not for the life of me figure out why the computer will boot up with 3 sticks of RAM when one of them is bad, but will not boot up if you have 2 or 4 sticks of RAM. I tried different positions so as not to have the bad one in dual channel with only 3 sticks in.

I think I just confused myself in that post

 

[mindless1]

Many bios will adjust some timings based on how many modules, so it could be that with 3 the bios relaxed a setting that improved stability, but even that wasn't enough once you load system down with 4 modules.