I was originally running 4GB (2x2gb) but figured I'd buy a couple more sticks and double my memory.
G.SKILL Ripjaws 4GB (2x2GB) DDR3 2133 F3-17000CL9D-4GBXL http://www.newegg.com/Product/Product.aspx?Item=N82E168...
After installing the two new sticks the system wont boot. Whats the deal?
More about :asus p8z68 pro 8gb 4x2gb memory wont boot
First, you cannot use XMP and the RAM MUST be set manually. Next, high frequency RAM in (1) kit should yield the Rated Frequency and CAS Timings. However, when mixing, yes this is a mix you might NOT get the Rated 'per set' Frequency and CAS. In addition, you are really pushing the IMC so the VCCIO Voltage might also need to be increased to 1.20v.
DDR3-2133 9-11-9-28-2N @ 1.60v
Next, in the BIOS manually set the Frequency, CAS Timings, DRAM Voltage -> 1.60~1.65v and the VCCIO -> 1.20v.
Failure, try a more standardized JEDEC -> DDR3-2133 10-10-10-30-2N @ 1.60v <or> 11-11-11-30-2N @ 1.60~1.65v and the VCCIO -> 1.20v.