So I built this computer back in 2007 and am just realizing that I'm running on single channel. I have a E6400 on a P5NE-SLI Asus motherboard, running 4x1gb of patriot extreme ddr2 800 RAM. I've overclocked my cpu to 333.4 Mhz x 8. Memory is running at 433.4Mhz, timing at 4-4-4-12, 2.24ish volts. Cpuz states I'm running at single channel. What gives? All four sticks of ram are identical.
In most, not all, cases DIMMs should be paired together. It's likely that you have installed your DIMMs slot by slot. Make sure you pair the DIMMs(RAM sticks). Your motherboard should be colored. Try just 2GB at a time, start with the closest DIMM slot to the CPU. Try that, The only other thing to do would be to check the POST and CPU-Z when you get into windows. Also, 4GB DDR2 is very cheap right now, that would maybe your last option.