Okay, your problem is that your board will only support 4GB sticks if they are Dual Sided sticks with 16 memory chips on them. The biggest single sided stick it will take is 2GB. You can view more about the memory specifications it will accept
here. You can also check the Memory QVL on that site to try to find sticks certified for your board, but they're probably out of production at this point.
Bottom line is if you want to get 8GB of RAM on your board, you're going to either need to get four 2GB sticks, or find double sided 4GB sticks for it to work.