I have a SONY PC (RX-580) and it is not booting on an erratic basis. The first problem was after pushing the start button, the fan starts on high speed, but no activity light and no HD light came on at all. AFter 1.5 minutes or so, I rebooted after removing the power cord for 30 seconds. This happened 8 times today. I should mention that during this time, nothing comes on screen at all. There is no opportunity to get to the CMOS settings or even to boot with a floopy. (yes this still has a floppy drive in it.) Normally, for the past several months, this problem has simply been an inconvenience and after 2 or 3 tries, the unit boots up fine and works fine all day. Today, when it failed to do this so many times, I shut it down, opened the case and proceeded to reset all cables and connections. I didn't notice any loose connections. I didn't remove ram sticks. I then rebooted and this time, I got the HD light activity for a few seconds, then the fan slowed to a normal level as like everything was going to be okay. After a few minutes, the activity light was still lit, but no flickering like something was happening. I turned the machine off again. I should mention that each time I turned the machine off, I didn't have to hold the button in for the normal 5 seconds. It turned of immediately. I once again, inspected and reseated cards. I did not remove RAM sticks. This time, I plugged in and booted and right away, got a 3 or 4 second solid warning tone, followed by about 3 seconds of silence. It repeated and kept going until I turned the unit off again. I suspected the power supply but I don't want to replace it until I know for sure. Do places test these power supplies or do they just replace them because of the cost of service? Any suggestions?