Purchased a refurbed 17" G5 imac from apple in March for my mum, but all of a sudden it has developed a problem. On start up I get the screen with the timer for about 10 minutes, then the fan will start and run for 3 minutes then go off, after a few more minutes the screen come up saying loading OSX and the blue bar takes another 10 minutes to reach the end. Then the screen loads, empty, then the icons and dock loads about 10 minutes after that. Once this process has finished , after approx 20 minutes it works ok. Any ideas why it takes so long to start up.