IMac display black when memory added

Question

My iMac had two 1gig sticks of memory. When Lion installed, I needed 4 gigs.
When I put one 2 gig stick in (meaning I have 3 gigs total now), display works fine. When I add the second 2 gig stick and turn iMac on, computer is on, but display is black. I have interchanged the new memory sticks by themselves in the imac to make sure they are both fine, which they are.
Soooooo......when I have either one of the new 2 gig sticks in (either memory stick--they both work properly), the display works, but when both 2 gig sticks are in, the display is black.
My model (late 2007) indicates computer will take 4 gigs total.
Please help!!!

Answer 1

Try resetting the SMC and pram/nvram
To reset the SMC
Shut down the computer.
Unplug the computer's power cord.
Wait fifteen seconds.
Attach the computer's power cord.
Wait five seconds, then press the power button to turn on the computer.
To reset the pram/nvram
Shut down the computer.
Locate the following keys on the keyboard: Command, Option, P, and R. You will need to hold these keys down simultaneously in step 4.
Turn on the computer.
Press and hold the Command-Option-P-R keys. You must press this key combination before the gray screen appears.
Hold the keys down until the computer restarts and you hear the startup sound for the second time.
Release the keys.