Ram Problem

[DaCosta5396]

Okay I have two problems:
1. either my pc boots in single channel memory mode with only 3.96GB ram usable
OR
2. it boots in dual channel mode with 8GB ram usable but when playing games like metro or bf3 I continually get a BSOD

RAM: Corsair CMX8GX3M2A1333C9 XMS3 8GB
Motherboard: AsRock 990FX Extreme3

Other Things:
Nothing is overclocked at the moment
I definitely have a 64-bit OS
Ram is definitely installed correctly

What would you suggest I try??

 

[cin19]

Test the RAM one by one with Memtest86 v4.0.

 

[DaCosta5396]

thanks for the quick reply...
i have no cd's at the moment..
is there anything i can try in the meantime??

 

[russianfool]

You can put memtest86+ on a flash drive if you have any of those, modern mobo's have no problems booting from one.

 

[DaCosta5396]

You can put memtest86+ on a flash drive if you have any of those, modern mobo's have no problems booting from one.

Passed with no errors
Any other ideas?