I have a pre-Intel iMac that I bought in 2005. 160G HD, of which I'm only using 21G, so lots of free space. I have maxed out my RAM at 2.5 GB DDR2 SDRAM (Speed: PC2-4200U-444), which my system profiler says is "OK." Other info: Machine Name: iMac G5 Machine Model: PowerMac12,1 CPU Type: PowerPC G5 (3.0) Number Of CPUs: 1 CPU Speed: 1.9 GHz L2 Cache (per CPU): 512 KB Memory: 2.5 GB Bus Speed: 633 MHz Boot ROM Version: 5.2.6f1 My Mac still runs pretty well. However, I can only run the machine by setting the Processor Performance speed to "reduced" in the System Preferences. Setting it to "Automatic" or "Highest" sees an incredible increase in speed, but within a minute, the machine goes into sleep mode or shuts down entirely. I run Onyx on at least a weekly basis to reset permissions and run maintenance scripts. I zap the PRAM on occasion. I don't have many widgets and never use Dashboard. I've checked the Activity Monitor and don't see anything maxing out my CPU (of course, I can't do this at the higher speeds as the computer shuts down, as I mentioned above). I keep the machine well-ventilated and free of dust as much as is possible. In short, I've done all of the suggested 55 steps to speed up one's iMac, I have a machine with little on it with tons of HD space available, I am current on software updates from Mac, I keep a super-lean desktop and have done just about everything one can think of to get more speed out of one's machine. Yet, I can't run the CPU at anything above reduced or my machine shuts down. Worse, I know that my machine could be running much, much faster if I could run it at automatic or highest speed, because I've seen it happen for those fleeting seconds before the machine shuts itself down. BTW - I'm pretty sure that I used to run the machine with the processor speed set at auto, but I set it to reduced a few years ago when this shut down problem started. I maxed out the RAM after that and hoped it would fix the problem, but it didn't. I AM getting much faster performance in reduced setting with the added RAM, but it still won't work above reduced. Any ideas on what could be wrong? I'm thinking that perhaps my machine is just too old and can't process 2010 info with 2005 guts. Your suggestions will be greatly appreciated.