ASUS Striker II motherboard problem

[HELOISE]

I am having problems with graphic card

my config:

Q 9500 4 X 2.5 GHz
Motherboard asus extreme srtiker 2
Two 9800 GX2 in sli
4GB DDR 3 (pc3-10600)
Windows Vista Premium 32-bit

When I start the PC with 4g of ram, Vista does not start.
With 3 GB of RAM vista starts but it only recognizes 2.75 GB (but I think it is normal)
When I added the 2nd card, vista not recognize me more than 2 GB of RAM, why ...?

I think these problems come from the motherboard can someone help me ?

Thanks

[Kaydence]

reinstall installation with vista 64bit, the latest driver for your motherboard and the latest nvidia driver and a bios update

[HELOISE]

I have already made several reinstall vista but no change and I have the latest drivers, including bios

[Caesar]

64-bit enable your 4GB to be recognized but if you did not have to buy is not a SHIFT you should try to save your bios CM a day against