You say you installed an OS ... but did you do a FRESH CLEAN INSTALL ? meaning not a copy from anywhere, not off another HDD, a true 100% from scratch clean install ? that often is a BIG issue with new builds. Also double check that your RAM and your CPU are all seated properly, especially the RAM since only the one side has the lock down tabs, you'd be suprised how many people don't set them in and lock them in place properly, and the excessive number of Error Codes and Issues that result from this.
As for your RAM clocks (1600 MHz /vs 1333 MHz) issue, in the BIOS set Mem Profile to XMP, that should help.
I'd also suggest you join up and post this in our Maximus IV GENE-Z68 Owners Club, lot's of smart help in there
ASUS Maximus IV GENE-Z68 Owners Club check it out newbie