ASUS P6X58D-E won't recognize all of my GSkill RAM

[jstaylor]

I have 6x4GB in my rig but only 20GB of the 24GB total is recognized by the system. Slot #6 shows as empty. I swapped the memory from slot #1 and slot #6 but I still only see 20GB and slot #6 is still missing. This is the exact memory: G.SKILL Ripjaws Series 8GB (2 x 4GB) 240-Pin DDR3 SDRAM DDR3 1333 (PC3 10666) Desktop Memory Model F3-10666CL9D-8GBRL

Thoughts?

[GSKILL TECH]

Seems like a bad motherboard if no memory is recognized in slot #6

Thank you
GSKILL TECH