I've had my PC for at least 6 months now, and it has worked fine. The other day, when I went to turn my PC on in the morning and it would power up for a few seconds (fans & hdd's whirring), before shutting down. It would automatically attempt a restart within a few seconds, but the same thing happens. I opened the case and had a look, nothing seemed out of place. I have tried it a few times since, and it can sometimes come on for a few seconds, and sometimes it will boot to windows and stay on for a few hours before shutting down again. In a nutshell: It powers up for intervals ranging from a few seconds to a few hours. I haven't changed anything in the system. I have tried a different socket & cable. I have ordered an Arctic Power 500W to replace my stock 300W, but I'm not wholly convinced it will solve the problem. Anyone got any other ideas, I'll take any simple-stupid suggestions, in case I missed something obvious. A common answer I have googled is CPU overheating - I highly doubt it is the CPU overheating in this case, due to it first occuring within a few seconds, and the PC staying on for a few hours at times. I have noticed the USB which I use for my mouse freezing during the longer stints that it is working, which makes me worry that it is the mobo, but the problem occurs whether plugged directly into the mobo, or using the case USB at the front, so this may be a symptom of a larger problem. Thanks for any help.