If you have trouble with your new RAM, check these things first.

Check the power cords. Is everything plugged in properly?
Check the module. Did both side clips snap to hold the module firmly in place? Try removing the module and replacing it to make sure it is seated properly in the slot.
Check the wires and cables inside your computer. Did you accidentally bump one of the cables inside your computer while you were installing your module? A loose hard drive cable can prevent your computer from booting up properly. Make sure all the cables are firmly in their sockets.
 
Step 9: Close your case.

Replace the memory access panel.
 
 
Replace any screws or fasteners that hold the panel in place.