a bit long this, but very strange ... My middle son lives in his own house. Yesterday he told me that his PC was not working, and described the symptoms, which were that when he switched it on at the wall, there was a clicking noise from the PC, the fans would start, then it would switch itself off, then there was the clicking noise, the fans would start, then it would switch itself off, etc, etc until he switched it off on the wall. I went over to look at it, disconnected the mouse, keyboard, monitor, removed the covers, switched it on at the wall, and sure enough it did what he said. So internally I disconnected the power-cable and sata-cable from the hard drive and from the DVD drive, and tried it again. Same symptoms. Next I removed the PSU. The cables were routed in all sorts of annoying places, loads of tie-wraps, and I had to remove the graphics card out of the way while I extricated the PSU, then I put the graphics card back. With the PSU outside the chassis, I switched it on without connecting anything to the PC. It clicked, and remained on. I switched it off-and-on, no click. I waited about 5 minutes, switched it on, and it clicked (so there must be a relay inside that latches on when the power rails are stable, and capacitors hold the rails for a while when switched off with no load). Then I connected the 24-pin cable to the motherboard and the 4-pin cable adjacent to the CPU, and switched on. Same symptoms as in the beginning. So I brought the PC and PSU home with me. At home I have a PSU tester, and I plugged the 24-pin into the tester and all the LEDs lit up on the tester. Same for the 4-pin and the sata power cable. I then plugged the 24-pin and 4-pin cables back into the motherboard, switched on, same symptoms as in the beginning. I switched off, removed the graphics card and all the leads to the front panel, switched on, and the green LED on the motherboard lit up and stayed like that i.e. waiting for the ON button. I shorted the ON-pins with a screwdriver, the PSU clicked, the fans started, and it all kept running. So I switched it off, plugged in the graphics card, plugged in a monitor and keyboard, switched on the PSU, shorted the ON-pins and it powered up and I got it into BIOS. Finally, I switched it off, plugged in all the leads to the front panel, switch on, pressed the ON button, and it all powered up and I got it into BIOS. I left it like that for 3 hours, and when I came back it was still sitting in BIOS. I have switched it on and off many times, and it all runs ok. I called my son later, and he says that before this all started, strange things were happening. The PC is 2 years old, it was Win-7 but it upgraded itself to Windows 10 some time ago, and in the last week things kept popping up on the screen and disappearing, it started to run very slowly, and the day before the on-off-on-off symptoms started, the mouse would not work sometimes, so he powered it off on the wall. The only anti-virus he has is free version of AVG, and he says he visits a lot of web-sites to get free movies. I reckon that there was (still is) definitely a virus/trojan in the operating system, and possibly someone was trying to install a virus into BIOS. But what I don't get is how the BIOS has corrected itself, and if it has, is there a virus in the BIOS now ?