Ram slots 1 and 3 not being enabled?

[chozen1]

I have 8gb ram ddr3, 2gb x 4, and it's all well placed im sure of it. My bios sees that all 4 sticks are in but only accepts slots 2 and 4 but 1 and 3 is apparently disabled or not working. So now my computer only has 4gb physical memory. How can I get the other 4gb to work? Please help.

 

[mubin]

How do you determine that slot 1 and 3 are disable? Where do you see only 4gb working? Form windows?