This board doesn't support 4 sticks.
It'll support 4GB kids that are made up of 2x2GB sticks in dual channel mode.
There is a way to utilise past 4GB in the advanced section of the BIOS (press F4 I think) but either way, it'll not be happy once all slots are filled.
Best results are with 1+3 (1,2,3,4)
It's an old issue, but I don't ever recall there being a way round it.
To double check it's all there, do the following:
1). R.hand click on "My Computer" and select "Properties". A new window will open listing you're PC's key hardware (CPU model, speed, ammount of RAM and version of Windows)
2). Download "CPUZ" and run that. Go to the Memory tab and you can look at all the slots individually. It'll list what RAM, if any, is being regitered in each slot as well as give you further information on them (speeds, voltages etc)
There is a 3rd, and that's what version of Windows do you have? If it's a 32bit OS then it can't see more than 4GB in total, that includes GPU RAM, BIOS, Page file, Network Cards and any other cards you have that have built in RAM. The average system will only ever see ~3.4GB due to a 512MB GPU, Page file and BIOS. The only way it'll see further is if you use a 64bit OS. (only Vista / 7 64bit is recommended, I mean, c'mon, Windows Live messenger made by Microsoft doesn't even support XP 64bit - I'm having to run aMSN open source
)
Hope that information is enough to help!
~Bex