Older System, 8GB RAM issue, please help...

Greetings, having a bit of a problem getting my kids computer to recognize 8GB of RAM. I currently have 3 sets of DDR2, they are as follows:

PC2-6400 OCZ2G8004GK - 5-5-5@1.8V
PC2-6400 OCZ2P4004GK - 5-4-4@2.1V
PC2-8500 OCZ2P10664GK - 5-5-5@2.1V
My motherboard is the Asus M4A77D, the PC is running the AMD Phenom 550 Black unlocked to 4 cores @ 3.1 stock speed, and these are the memory settings in the BIOS:

Memory Clock Mode = Auto
DRAM Timing Mode = Auto
Memory Overvoltage = Auto
Chipset Voltage = Auto
HT Freq = 2000MHz

My issue is that I cannot get 8GB to register regardless of the combinations of RAM sticks that I run. Each set indiviually runs just fine, and registers at 4GB in slots A1 and A2. I currently use the PC2-8500 set, and the other two sets stay in their packages. I am curious if these sets will just not work together? Or is there a memory setting that I may need to adjust in the BIOS? If there is any more info needed please ask. The reason I tried adding the extra RAM is that when the kids use the PC, on occasion, it will lock up for about 60 seconds and then resume. If they are playing BF3, it will kick them from game, and Battlelog will show a "You have been kicked from the server" message. Initially I thought it was a reserved slot kick issue, but it happens when they are out of the games also. I assumed that perhaps with the resident programs running, the RAM is running out, and that maybe 4 more GB might do the trick, alas, I cannot get 8GB to register with the combined sets I have. When I go into the 'DRAM Timing Mode' section of the BIOS and change it from auto to manual, I get like 30 options in a list that look like this: TCL, TRCD, TRP, trTP, etc etc etc. When I go into Memclock Mode and set from auto to manual, I get options of 200,266,333,400 and 533 MHz, but that is it. Still a bit clueless as to how to change those settings based on what I am seeing in the BIOS, when it comes to adjusting timings, voltage, etc.

I appreciate any help you may have for me in advance.