Late 2011 Macbook pro - Wont recognize 8gb memory

Hello Apple users,

so heres my problemo. I recently purchased this item . http://www.amazon.com/gp/product/B002YUF8ZG/ref=oh_details_o00_s00_i00?ie=UTF8&p sc=1 .

Corsair 8GB (2x 4GB) 1333mhz PC3-10666 204-pin DDR3 SODIMM Laptop Memory Kit CMSO8GX3M2A1333C9

For my 2011 Macbook Pro 13" 4gb. I Installed both sticks and turned it on, white/gray screen with apple logo shows up underneath it is a spinning white wheel and it spins for a bit then stops and nothing happens it just stays frozen like that. Now when I take one of 4gb sticks out and put a stock 2gb stick in, it loads and the computer turns on and recognizes that I have 6gb of memory. so im thinking okay maybe I have a faulty stick, but then I try the other 4gb with a stock 2gb and it works also.. so now im thinking okay maybe I DONT have a faulty stick.. so then whats the problem ?? I put both back in again in different slots and still not able to load. Am I not waiting long enough for it to fully load ? like does it take more than 5 mins to first start up? or is the speed on my macbook not capable of letting this load idk?

does anybody have the same problem and was able to solve it?

Any info will help, im about to start a new job and I need my macbook to be quick running multiple apps and having the extra storage helps.

thank you in advance!