Starting issues with iMac 27 i5 quad after crucial RAM expansion

Question

I have read through a few threads regarding issues with crucial RAM upgrades in iMacs but they don't quite match what I am experiencing.
I have installed 2 x 2 GB Crucial RAM (manufacturer 0x80CE) in addition to the pre-installed 4GB. The iMac works fine without any glitches, freezes or crashes. However, when I try to start it up in the morning I can hear the HD starting up and stopping once. The start chime doesn't sound and the display stays black. I take out the 4GB and the computer starts up without any problems. I then switch it off again, install the other 2 RAM again and lo and behold: all works fine. Until the next morning. I do not entirely disconnect the iMac, which is an Apple refurbished machine, I just switch it off.
The first time that happened, I thought it was another problem like USB, bluetooth etc. So I systematically disconnected and reconnected all peripherals, I even used a USB mouse and keyboard and tried to start up from the restore DVD. So I went through all that pain.
If there is an existing thread I would appreciate if you could point me in the right direction because I couldn't find anything like this on this forum.

Answer 1

Did you test all 4 modules one at time in a top slot as suggested, to see if they are all working?
● If any one of the modules fail to properly boot the iMac, factory or crucial then do not reinstall it into the iMac.
● If all of the modules individually boot the iMac, then try reinstalling the Crucial in the top slots, the factory in the bottom slots and Startup the iMac reseting the PRAM.
http://support.apple.com/kb/HT1379
+1. Locate the following keys on the keyboard: Command, Option, P, and R. You will need to hold these keys down simultaneously in step 4.+
+2. Turn on the computer.+
+3. Press and hold the Command-Option-P-R keys. You must press this key combination before the gray screen appears.+
+4. Hold the keys down until the computer restarts and you hear the startup sound for the second time.+
+5. Release the keys.+
Now then if the iMac is not booting from all 8GB of RAM, then there is a compatibility problem with the Crucial RAM and you need to contact Crucial and tell them that there Ram is not working with your Factory RAM.
Why would you only want RAM in the bottom slots, I thought the idea here was to upgrade from 4 to 8GB?
The article clearly states that the iMac will not boot with only 1 module in a bottom slot.
http://support.apple.com/kb/HT3918