I have an imac, it has a model number M5521. It has also got the following information on the sticker: Imac 600/sn/128/40/cdrom/ultra/56k/fw/vga. I don’t know much about Mac as I am mainly a PC user. However I was working on the mac when it turned it self off and now it wont start. When I press the power button I sometimes hear the cd drive starting up – it may be starting all the time. There is a green light on the logical board which is on. The battery is reading 3 volts, is this enough or should I replace it? There power light on the switch does not go on; unless I hold the power button in for about 10 – 15 seconds then the power light flashes. There is no output through the screen. There is no sound. Can anyone help? Thanks I have tried the following things: The Imac is the slot cd rom drive. There is nothing plugged in except the keyboard, mouse and power cable. I have tried replacing the power cord. I have tried a different power outlet It doesn’t start up when I unplug the keyboard and mouse I have reset the PMU and it hasn’t worked. When I reset the PMU when it connected to the main power, lots of lights flash but nothing else happened.