iMac RAM issue

I recently purchased two Kingston 2GB sticks of DDR2 RAM to replace my one stick of 1GB DDR2 RAM. So I removed my 1GB stick and replaced it with a 2GB stick and put another 2GB in the empty slot. But my computer refused to boot up. So I switched out one of the 2GB with my old 1GB and it works perfectly, even says that both sticks (the old and one of the new) is working OK. so i switched out the 2GB with the other 2GB and it still worked fine. The computer only had problems when both of the 2GB sticks were in. Why would this be?

same problem

Yes, it is exactly the same problem i had i really need a answer. I have imac 7.1 at apple's site it says imac 7.1s can support 4 gb with 2 X 2 gb sticks but it's not the case help will be appreciated. thanks

Return the RAM and get something else if it doesn't work. If you're buying the cheapest RAM you can find, it may not work. Macs can be a little picky with RAM.

Either stick with some solid name manufacturers and their higher end memory or head for sites that sell memory known to work with Macs such as Crucial or OWC. OWC is pretty good and you can find lifetime warrantied RAM within just a couple of dollars of the cheap junk you'll find on newegg.