My 15" macbook pro specs: Model Name: MacBook Pro Model Identifier: MacBookPro4,1 Processor Name: Intel Core 2 Duo Processor Speed: 2,4 GHz Number Of Processors: 1 Total Number Of Cores: 2 L2 Cache: 3 MB Memory: 3 GB Bus Speed: 800 MHz Boot ROM Version: MBP41.00C1.B00 SMC Version (system): 1.27f3 i needed to upgrade my memory as i use my mac for 3D work, so i checked and from what i could find my mac supports up to 4GB. the only prob was that i cant get 667mhz memory anymore (i live in S.A) so i bought a 2gb kingston kvr 800mhz stick and it worked perfectly (specs above with the new installed 800mhz ram). my mac downclocked it to 667mhz no problem. so i bought another 2Gb stick thinking that it would just do the same. however when i put it in i just get a blank screen at start up. (the new ram does work, i checked it by swopping it with the other 2gb kington ram and it works fine) i looked around and found that because i didnt have at least one of the original 667mhz sticks in, my mac wouldn't automatically downclock the 800mhz ram to 667mhz. is this correct? if so is there a way to manually downclock the ram? or is there ANY way at all to get around this? any help or suggestions are much appreciated!!!