ASUS P5N-E Sli 4 ram slot usage, help plz ;(

hi guys.

Operating System: Windows Vista 64x™ Home Premium (6.0, Build 6001) Service Pack 1 (6001.vistasp1_gdr.080917-1612)
Language: English (Regional Setting: English)
System Manufacturer: System manufacturer
System Model: System Product Name
BIOS: Phoenix - AwardBIOS v6.00PG
Processor: Intel(R) Core(TM)2 Quad CPU Q6600 @ 2.40GHz (4 CPUs), ~2.4GHz
Memory: 4094MB RAM
Page File: 1473MB used, 3559MB available
Windows Dir: C:\Windows
DirectX Version: DirectX 10

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Display Devices
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Card name: NVIDIA GeForce 8800 GT
Manufacturer: NVIDIA
Chip type: GeForce 8800 GT
Display Memory: 2795 MB
Dedicated Memory: 1004 MB
Shared Memory: 1791 MB
Current Mode: 1440 x 900 (32 bit) (60Hz)

OK so i bought this pc about a year ago and it works fine. but i have another 2 slots for ram so i might as well use them. This mobo supports up to 8GB of 800mhz DDR2 ram. so i have got 8GB brand new OCZ DDR2 6400 ram right now, but when i try to install more then 2 sticks of ram the pc wont boot. here is what i have tried. here is the layout of the mobos ram slots and what i have tried and tested to try and sort this out-

1x blue ram slot
1x yellow ram slot

1x blue ram slot
1x yellow ram slot

Test1: swapped out all 4 modules in first blue ram slot - all work fine
Test2: 1 module in each of the blue ram slots - all work fine
Test3: 1 blue and 1 yellow slot filled - pc wont boot up, it powers up but monitor wont even come off standby.
Test4: 1 blue, 1 yellow, 2nd blue ram slot filled - same result as above
Test5: All ram slots filled - same result as above ;(
Test6: single module in a yellow slot - wont work...wtf???

ok so i have confirmed that all 4 ram modules are working fine and dandy. but it seems that when i try to use the yellow outlined ram slots the pc just refuses to boot up at all.

any ideas mates?

You have to increase the Northbridge voltage.
Increase memory voltage to 2.1v. Relax timings.