I've got a self build AMD system with a 550w cheapo PSU. This PC has lasted me a good 4 years now but recently, its been shutting down on its own. It can vary from a few mins from start up or a few hours. The system shuts down as if the power has been cut but the LED on the case remains lighted up. The only way for me to switch it on again is to turn off the mains power. Yesterday I could not get 2 mins use once logged into windows but today, after 3 tries, it managed to stay on. Is this pointing towards a PSU problem or something else?