I bought 2 1gig sticks of ram from Crucial for my iMac (specs below). Pulled out the old sticks, installed the new ones. Pluged everything back in, powered it up, and nothing. Well, it did make some sounds (something spinning up) and the power indicator light came on and stayed lit. But that was it. So, messing around with it I discover it will work with either stick by themselves, or with one of the old Apple sticks (512) and one of the crucial sticks, but not both crucial sticks. I talked to Crucial and they have no idea what the problem is. But they are sending me out high density ram, and maybe that will make a difference. I can't call Apple because it's 3rd party ram. I was wondering if anyone here had heard of this, or had any ideas. If the new stuff Crucial sends out doesn't work, I guess I'll have to buy some Apple ram and see if I have the same problem.