Hi I am using an ASUS M5A78L-m/USB3 Mother board with 4 dimm slots. DDR3 PC3 12800 1600mhz. Using windows 7 64bit OS.
Currently 2 slots of 2gb being used. Just tried installing 2 x 2 more gb of same ram. Initially would only accept 1 of the extra ram and in windowes showed 6gb intsalled, 4gb usable. When try putting 4th in it just gets to windows boot screen and crashes(blue screen of death). I altered bios so that all ram settings eg remapping interlacing etc are auto and now i have windows saying 6gb available. But when i try install the 4th bit of ram it still crashes so wont accept full 8gb.
What confuses me though is before windows tries to boot is shows 8gb in bios when i put the 4th bit in!!
Try to see if it happens with the SAME RAM module every time.
Also, try to see if it happens with the SAME DIMM slot on the mobo every time. That could help narrow down the culprit (RAM stick or DIMM slot on the mobo).
You might consider upping the RAM voltage a tiny bit beyond 1.5v because most RAM prefers 1.6v (or even 1.65v).
Of course this is no 'solution' if you in fact have a bad stick...
Also make sure your M5A78L is running the latest BIOS (which will enhance memory compatibility).
You can up the clocks on the RAM to make it run at 1600mHz in the BIOS for most motherboards, but it's not worth it unless you want to squeak a little more out of it for synthetic benchmarks. For everything else, you won't even notice a difference between 1333 and 1600.
Also, if a motherboard supports faster RAM, it will usually show this on a RAM QVL and they'll advertise support for higher, but it sounds like your motherboard supports a max of 1333.