Q: Please help! "This version of OS X 10.10 cannot be installed on this computer."

The 2 places I’ve seen recommended most to buy reliable RAM are below. I have purchased RAM several times from Other World Computing and have always been very satisfied with the product and service. They have on-line instructions on how to replace the RAM. OWC has also tested RAM above what Apple states is the maximum. I now have 6GB installed on a early 2008 iMac supposedly limited to 4 GB and noticed an improvement.

Crucial

Other World Computing

Hardware Overview:

  Model Name: iMac

  Model Identifier: iMac5,1

  Processor Name: Intel Core 2 Duo

  Processor Speed: 2.16 GHz

  Number Of Processors: 1

  Total Number Of Cores: 2

  L2 Cache: 4 MB

  Memory: 2 GB

Can I run El Capitain Kurt?

OS X El Capitan - Technical Specifications

Sorry, no. Yours is a Fall, 2006 model. It maxes out on Lion, 10.7.x.