I have one of the earlier intel core duo imacs, not sure how early. Today I've gone out and purchased 4GB of DDR2 667 ram (2 x 2GB), to upgrade from my existing 2 x 1GB. On installing the full 4GBs of ram I get a black screen with a constant white light. If I try the 2GB sticks individually and they both work fine, so both sicks of ram appear to be fine. I've also tried a 3GB combination using one 2GB new stick and one 1GB old but this gives the same black screen. I've a bad feeling that I may not be able to upgrade my ram beyond 2GB so I've wasted my cash and time. I know the Leopard OS is 32bit but I was hoping that I could put 4GB and this would at least give me 3GB? According to this http://support.apple.com/kb/ht1432 I may be unfortunate to have one of the earlier macs that can't handle over 2GB, but I don't know how to tell? Can anyone suggest a solution or work around, to resolve my issue and get both new sticks of ram working, or am I trying to do the impossible?