Difference between PC-4200 and PC2-4200?

DDR2 was the correct memory to order. Did you use an online memory configurator that showed you the correct RAM, or did you just pick some off a web page? I hope that you can exchange it at no cost to you.

I wouldn't rely on what's printed on an order form, as I don't believe there is such a thing as DDR2 PC-4200. I'd be looking at the sticker on the RAM and at the website product info to make certain you received what you meant to order.

Mitch,

It looks as if you ordered the right stuff. As long as it easily fits into and matches the geography of your slot you should be ok. In that case the RAM appears to be either DOA or not compatible with the existing RAM. If it has never been recognized by the system, I would assume that means DOA.

Again, I wouldn't pay any attention to that wording, it looks like a typo that left out a single digit "2." If you look around at other sellers' websites you'll see that there really is no DDR2 PC4200 533MHz RAM, it's all DDR2 PC2-4200 533MHz.

I went to the website and see that your supplier is someone that I seem to recall has been recommended by others on these boards. Keep in mind that at that price this stuff is just not pre-tested or anything. It's simply shipped out hot off the assembly line. Therefore, a certain percentage of the production are simply not viable, which is recognized by the fact that they are providing a replacement/refund warranty.

I note that you're otherwise happy with your new iMac. Have you used the version of "Disk Utility" in your Applications>Utilities folder on your HD to run the "Repair Permissions" procedure on the entire HD?

After you open Disk Utility, you want to be in the "First Aid" section. Simply select (highlight) your entire HD and click the "Repair Permissions" button. It should run through in less than a minute. You really should do this simple procedure both before and after installing software and hardware.

Since you had at least two kernal panics and had to do hard shut-downs, you also should run the "Repair Disk" procedure. Install your original install disc, restart and hold down the "c" key of your keyboard, and your iMac will boot to the install disc, without the OS controlling your system. Get past the language choice screen, then at the top of the screen under the "Utilities" pull-down select "Disk Utility" and once again select the First Aid section and your entire HD and click on the "Repair Disk" button. It should take well under a minute and should be rerun until the report states "No repairs necessary"

While your iMac is new and problem free is a good time to familiarize yourself with it, so I'd also recommend running the Apple Hardware Test that is also on your install disc set. You should have no report or message of any error or problem - you can view both panels of the Test both before and after running the extended Test. Since you have only the original 512MB of RAM it won't take as long to run as it will once you install the extra 1GB. Probably less than 30 minutes now, and you'll notice the fans are free of software controls while booted from the Test disc.