Problems adding 4GB Ram to 24" iMac

[kn]

I have two 2GB sticks but my iMac will only recognize each one separately, not together. When I have 4GB installed, the machine doesn't start.

My iMac is from January so it should be able to recognize 4GB. I know previous models had a 3GB limit but I really thought my model was new enough not to worry about this.

My specs:
Model Name: iMac
Model Identifier: iMac7,1
Processor Name: Intel Core 2 Duo
Processor Speed: 2.8 GHz
Number Of Processors: 1
Total Number Of Cores: 2
L2 Cache: 4 MB
Memory: 3 GB
Bus Speed: 800 MHz
Boot ROM Version: IM71.007A.B03
SMC Version: 1.21f4

Any ideas would be appreciated. Thanks.

[Barnes]

Even if it was a 3 GB model the machine should still start and not address the extra gig.

[kn]

What would this be a symptom of? Each chip works separately with one of the 1GB sticks that came with the machine.

[Traditional_Ale]

Is your operating system 64-bit?

You need a 64-bit operating system to utilize 4 gigs of RAM.

[Vulcan]

Maybe not applicative to Mac, but have you set the voltage and timing and speed in your bios for your particular ram?

[Barnes]

Originally Posted by Traditional_Ale

Is your operating system 64-bit?

You need a 64-bit operating system to utilize 4 gigs of RAM.

Not with OS X. The transition isn't as cut and dry as with Windows. 64 bit support started with OS X 10.3 and allowed for addressing more than 4 gigs by allocating it in 32 bit chunks.

The iMac 7,1 should be a max of 4gb. Try turning on the machine by holding down Cmd-Option-P-R to reset the NVRAM and PRAM.

[Barnes]

Originally Posted by Vulcan

Maybe not applicative to Mac, but have you set the voltage and timing and speed in your bios for your particular ram?

Mac's use EFI.

[kn]

FWIW, it turned out to be the wrong type of memory.