XFX Nvidia nForce 780i mobo memory problem

Hey, I recently bought a new XFX MB-N780-ISH9 LGA 775 NVIDIA nForce 780i SLI Intel Motherboard and everything works great on it except 2 of the memory slots. When I put memory in DIMM slots 0 or 2 it will boot up fine, but if I put memory in DIMM slots 1 or 3 I get the long beeps and a C1 code on the mobo. The memory I am using is the CORSAIR XMS2 2GB (2 x 1GB) 240-Pin DDR2 SDRAM DDR2 800 (PC2 6400) Dual Channel. The first time this happen I thought the 2 slots were bad, so did a RMA and got a new board, but it still does the same exact thing. So Im pretty sure it has nothing to do with the mobo itself. I talked to the Xfx support and they said to try different memory or it could have something to do with my power supply. But before I buy different memory does anyone have any other ideas of why this is happening?

Here are the specs of my PC:

Motherboard: XFX nForce 780i MB-N780-ISH9 [url=http://www.newegg.com/Product/Product.aspx?Item=N82E16813141005][/url]
PSU: Rosewill RX950-D-B 950W
CPU: Intel Core 2 Quad 6600 G0 LGA 775
Memory: 2Gb (2 x 1Gb) Corsair XMS2 DDR2 800 [url=http://www.newegg.com/Product/Product.aspx?Item=N82E16820145177][/url]
CD/DVD-RW combo drive
Western Digital 7200rpm 500gb SATA 3.0Gb/s Hard drive
1 ZOTAC Nvidia 9800GTX 512MB PCI-E graphics card
Sound Blaster Audigy SE PCI sound card
Arctic Cooling Freezer 7 Pro heatsink
4 x 80mm case fans

Thanks for the reply. I thought my PSU might have something to do with it. I will try out a new one soon. Iv been looking at this Antec 1000W [url=http://www.newegg.com/Product/Product.aspx?Item=N82E16817371012][/url] . Think that is good and can handle the specs of my PC plus handle SLI later when I buy another video card? Any other suggestions are appreciated.
Thanks