I was gaming on about a 2yr old build when I paused a game to take a phone call. The screen went dark, the computer seemed to power down. But the PSU switch was obviously still on but I noticed my speakers pop every few seconds and my mouse light up at the same time. I could tell something was stopping the PSU from constantly supplying power. I have a warranty on the PSU, so I exchanged it for a new one. However, I'm having the exact same issue upon turning on the PSU's switch. In normal operation before this issue, my mouse lights up when the PSU is turned on, even when my PC may be off. I timed the light coming on at about 2 seconds between lighting up. And when it does light up it barely comes on before turning back off. Since I have replaced the PSU already, is there a better way to test what might be going wrong?