Problems with RAM installation

Hey, today i just got a new 4gb memory stick to add to my computer, currently i have 2 2GB DDR3 1333 RAM sticks.(These were both Kingston Memory Sticks) I then added a 4gb DDR3 1333 Ram stick (Crosshair) to the motherboard and made sure they were firmly placed in and it was all fine, I then turn on the computer and find that the motherboard starts beeping once then two beeps after and the Screen is blank, and my mouse & keyboard aren't responding. My current OS is Windows 7 64 Bit, so i shouldn't have a problem installing new ram to my system...
I'm not sure if this is a problem with 2 different brands of sticks or what.. but the fans are running for my Graphics card (I don't have onboard graphics available)

Specs
AMD 1055t X6
ASUS M5A99XEVO Motherboard
ATI Radeon 5570
Kingston

Any help anyone? Thanks
-Joe

The motherboard does not like that 4GB module. Have you tried the 4GB by itself? If the 4GB module won't run the computer you'll have to stick with 2GB modules. How many memory slots are on the motherboard? ASUS motherboards are notorious for being very picky about memory

I'm with Tmagic and standing behind what he said.

Are the voltage requirements the same for all modules?

Its fine now, for some reason it decided to work.. i just took them all out and back in again, (i allready did this about 5 times) and it just started working... i have no clue why xD. but now the computer is running fine i got 8 gig in there now. And my PSU is a 750 watt so there shouldn't be any problems ^^. Thanks for the replies