I might be able to help, but maybe not. First of all, that motherboard in particular, and practically all motherboards using that chipset, can be a little "extra difficult" to get into Dual-Channel mode.
First thing you'll want to do is remove the old RAM, since you need matched pairs to run dual-channel.
Try booting one module in Slot 2. If that works, go into BIOS and increase the first three latency values by value (for example, 2.5-3-3 to 3-4-4), and increase the memory voltage to 2.8v. Reboot, then shut down and install the other DIMM in Slot 4.
If that works, do some testing. If everything comes out stable, try lowering your timings, one at a time, in reverse order. IE, change the 3-4-4 to 3-4-3, retest, then try 3-3-3, retest, then try 2.5-3-3. If you can get back to the original timings using only the increased voltage, great. If you can't get back to the original timings but it's stable with the higher timings, well, at least it's stable.