Does it still boot with your old original RAM in there?
Install and remove the new sticks several times (3-5 times), so you rub off any oxidation that forms on the RAM pins and contacts.
Also try booting with only one stick at a time...the other may be faulty.
--
G74SX-CST1-CBIL, i7 2630QM 2GHz
32GB DDR3 RAM @1333MHz
GTX560M 3GB DDR5 (192 bit)
17.3" LED 1920x1080
Sentelic TP, BIOS 203
Debian Linux Wheezy (Testing) Kernel 3.2, NVIDIA 295.40