My PC monitor began pixellating while in use and PC froze. Powered down by holding in power button and tried to power it up after allowing it to cool down. PC worked for about 10 minutes and repeated the same symptoms. I assumed it was the video card. I bought an identical card and installed it. When I powered it up, all it did was sound a continuous tone similar to a smoke detector. No fans revolved and nothing appeared on the monitor. I'm assuming that the 375W power supply needs to be replaced. Note that this is a nine year old PC but I need it brought back to life. Please help diagnose what the issue could be.