My Toshiba Qosmio X500 laptop shuts down before booting. After pushing the power button the power button and caps lock button lights up, then turn off right away. Then, without even pushing the power button again those buttons light up and turn off repetitively. At the same time the left fan is gently running, then turns off, then repeats this. I had recently changed the motherboard since a computer store told me it is defective. The source for the MBO insists it was checked and working properly before sending it to me. Someone told me perhaps the power cord is defective, though not sure I want to buy another one unless this is the problem....also not easy to find one. Same thing with a replacement video card...not sure if that is the problem. Sounds like a short somewhere, or perhaps one fan doesn't work properly, though I don't know why that would stop the laptop from booting up. Twice recently the fan ran louder for a few seconds, then shut off. One repair person gave the laptop back to me since he could not fix it, and at least didn't charge me. In the meantime I bought another laptop, but still would like to get the X500 working again as a backup, since it was great for many years....before Toshiba threw in the towel on laptops and support.