New memory modules causing Macbook Pro (Early 2011) to not work.

My macbook pro memory specifications are "Apple Memory Module 4GB 1333MHz DDR3 (PC3-10600)" I Bought two PNY 4GB 1333MHz DDR3 PC3-10666 modules to upgrade to 8GB of RAM. I installed them, turned on my comp, everything worked fine, but when I looked at the memory it said only one slot was filled and it had 4 GB. Thinking I installed one wrong, I opened it back up, removed them and put them back in. Then when my mac started it was all messed up and pixelated, and beeped 3 times. Totally unusable. So I tried again with just one of the 4bg memories in. Then it was totally screwed up again and beeped once. I continued to try every possible combination, one 4gb, one 2gb, even to get back to where it only recognized the one 4gb but still worked... no matter what, if either of the 4gb were inserted, it would not even start up and the screen was all messed up. Finally, I put the original 2 GB rams back in (4gb total) and then my computer worked as normal. I want to try to take it to best buy and see if they can install the new ram and get it to work, or maybe I need different RAM.. anyone have any idea what happened there? I have a MacBook Pro (13-inch, Early 2011).