Hello, I have windows 7 64bit. Asus P6T Deluxe V2
Crusial Ballistix DDR3 (3x2 2gb)
1600 MHz ( PC3-12800 )
In BIOS :4088 MB ram
In Win :4,00 GB ram
In CPU-z:6144 MB ram
On the ram kit it is fitted some kind of heat-sink with LEDs witch I assume indicate that they are "working/thinking". DIMM_A1 & A2 seems to doinf their thing, C1 is "frozen" (the LEDs)..
Run memtest86+. If you get any errors, run it using only one stick at a time. I bet you will find a defective stick.
If, by chance they all test out well, test a known good stick in each slot to test for a bad slot.