I though maybe mixed memory speed until i saw this on the web from junejuly
''The latest P77 bios (1206 for me) is an absolute disaster. Only 8 of 16GB RAM showing for many, del to get in bios doesnt work (have to use the num pad del) PCIe 3 issues etc. You really should rollback. ''
Motherboard talked about was ASUS P8Z77 V LX but im 99% positive they share same memory settings at bios .
Which bios you are using now ?can you update bios ? Asus bios update needed done carefully ,any friend can help to you?
Also look here http://vip.asus.com/forum/topic.aspx...Language=en-us