System won't post with 4 sticks of ram

[Echo42]

So I'm building a new machine for my office, Gigabyte M61PM-S2 motherboard. has 4x DDRII ram slots. I purchased 2 sets of matched pair 1g Corsair ram (listed as supported by Gigabytes website).

When i put in ram pair 1, sticks A+B, everything posts just fine.
If i add in pair 2 stick A with pair 1, everything posts fine
If i have in pair 1 A+B and pair 2 stick B, everything posts fine.

However if i have in Pair 1 A+B & Pair 2 A+B, i get no post

Ive tried all the sticks in the 4th slot, and nothing will get it to post. Is it a bad ram slot? am i doing something wrong? The board supports up to 16gb of ram, so its not that I'm putting too much in...

any help would be greatly appreciated.

other information if it matters/helps:
all parts brand new
4x Corsair CM2x1024-6400
Gigabyte m61pm-s2
Athlon Sempron 3600+
WD SATA HD
LG DVD-RW

thanks again!

 

[Oxides]

You can test if the 4th slot is defective pretty easily. Installl a matched pair in ddrII_3 and ddrii_4, with ddrII_1 and ddrII_2 empty. The computer should boot up.

Assuming the above test worked ok, I would boot up with 2 sticks and change the memory timings from auto to some looser settings then try and boot with 4 sticks in.