My Dell is a 2011-05-23 model with Win Pro 7 - and 4 memory sticks in it. Its run b\pretty well up to now. A couple of times it did not boot up put shutting it down and restarting it - it came right up. Today my wife was using it and it just shut down. ok - my computer does not have 4 lights on it like most I have read about. I took it apart and cleaned it up - it wasn't that dusty. \r\n1. When you push the power button the computer fans inside start to spin - there is 4 fans in the machine. 1 to 2 seconds later they all shut down \r\n2. There is a pause for like 5 seconds and you hear the fans kick in again for 1 to 2 seconds and again they shut down. this will continue if you don't push the power button and hold it for 10 seconds.\r\n3. When you plug the tower in there is a green light on the back of the computer by the plug that does come on in green color and one on the mother board in yellow with writing by it - AUX pw4.\r\n\r\nFrom the different posts I see things like unplug the fans to see if they are shorted.\r\nPull all the components and re-seat them, still didn't work.\r\nPull the battery and wait a few minutes and replace it and then try - didn't help.\r\n\r\nSo how can I tell is it the motherboard that is bad or the power supply that might be bad. also read somewhere it might be the power on/off switch. any help or ideas would be great full - yea the warranty has run out and from what I can make out dell wants 239.00 dollars to let them diagnose it.