Hello, I'm having this strange problem on my Imac, it is after all 3 years old but it still shouldn't happen. Since it has become very slow I've checked the memory and it's completely empty. Approx. 30mb free and 200 passive, the remaining 1700 are "used". The strangest thing is that none of the processes in activity monitor display this usage and after all I'm only running safari and word. Any ideas where to start my research? HD has 100gb free.