2009 iMac beeps at startup

My iMac 10,1 Late 2009 27" iMac Core 2 Duo (E7600) beeps on boot up. Thinking it is the RAM I tried putting each two (2x4GB) 8GB G.Skill FA-10666CL9D-8GBSQ kits into each memory slot. All two (2x4GB) 8GB G.Skill FA-10666CL9D-8GBSQ kits works on the originally unused slots. The slots occupied by the default memory from Apple will not accept any of the two (2x4GB) 8GB G.Skill FA-10666CL9D-8GBSQ kits.

Should I consider resetting NVRAM / PRAM?

Its worth a try.

Thats an odd problem, have you tried mixing up the pairs? Could be one stick has gone bad.

What kind of beeps? Is it a set of three beeps, and is it successfully booting?

Is your iMac qualified to run this RAM? It doesn't sound right. The G.Skill web page

G.SKILL- World leading DDR3 computer memory and SSD manufacturer -Products

does not list your model of iMac for this RAM. In fact it says this 1333 MHz RAM requires an i3/i5/i7 processor and a Core 2 Duo iMac (yours I think) can only use 1066 MHz RAM. I think you are using the wrong RAM for your iMac model. That's why it won't start up properly. The beeps are probably telling you something is wrong with the memory.

The model numbers given contain 1066 as part of their designation. How could that possibly be used by any sane company for 1333MHz RAM?

In many cases the 1333 is backwards compatible anyway.

The manufacturer lists the speed as DDR3-1333. The manufacturer also lists the compatible Macs and the original poster's is not listed there for these chips. His computer is not booting properly with these chips in there. I'm suspecting he is using the wrong chips for his Mac. He has done the same thing (wrong memory chips for his model) in other posts twice for other computers elsewhere in these forums.

Waragainstsleep mentioned faster memory can work on slower systems. The system just clocks them down. That's why everymac.com states "Min. RAM Speed:" in their spec sheets.

Faster modules could work on slower Macs.

F3-1600C10D-16GSQ DDR3-1600 kits on Macs that require DDR3-1333 memory modules.

1) MacBookPro8,1 Early 2011 13" Core i7 (I7-2620M)
http://farm9.staticflickr.com/8186/8...f1329fb8_o.png

2) Macmini5,2 Mid-2011 Core i5 (I5-2520M)
http://farm9.staticflickr.com/8518/8...feffd720_o.png

3) iMac12,1 Mid-2011 21.5" Core i5 (I5-2400S)

I have also successfully installed FA-10666CL9D-8GBSQ DDR3-1333 kits onto Macs that require DDR3-1066 such as

1) MacBookPro5,1 Early 2009 15" Core 2 Duo (T9550)

2) MacBookPro5,5 Mid-2009 13" Core 2 Duo (P8400)

I agree with you that it CAN work. However when the manufacturer lists compatible Macs and your Mac isn't in that list, I think the result of using that RAM could well be boot up problems or other anomalies when doing intensive processing -- exactly the symptoms you are seeing and you have posted about. Why would you put higher speed RAM in when the manufacturer does not recommend it (they could have easily included the other Mac models in their recommended list)? Even if it runs, you'd never see any advantage if they just get clocked down anyway.

By the way, it never hurts to reset PRAM or NVRAM as you asked about, and there is a small chance it might resolve one of the issues you were having.

Bulk order discount. Anyhow will be returning whatever doesn't work. Thanks for the help. :)