I have a 2008 iMac and there is no "About this Mac" option when I click on the Apple icon. So, how do I find out my serial number, year make, processor, etc?

If you can't click the Apple Logo to find your system information, you'll have to go into Launchpad or Applications if your on a older version, click on Utilities, and click System Information. This should give you an advanced view of your hardware and model.

What OS version are you running?

And, can you send a pic or screenshot of the drop down menu under the Apple please.