I plugged in a usb drive which it detected as having a virus. It's done that before with this file on it but i believed it was a false positive and have ignored it many times before.
Moments later Avira detected another suspicious file, this time in temporary files.
I carried on what I was doing but then things started messing up... First I couldn't click on any files in an explorer window but everything else was fine, then it started happening with other Windows, including Avira. Then I couldn't click on the start menu to restart. Nothing was frozen or not responding, it was as if my mouse button wasn't working.
I turned the PC off manually and now when I turn it on nothing happens. Just a black screen, no BIOS or anything. It won't even let me turn it off my holding the power button, it's just dead. No beeps.
I've removed the processor and RAM and put them back, checked cables etc. All seems fine.
Given the virus detection, I'm inclined to think it's not a hardware issue.
I've used a couple of USB rescue disks for viruses with no joy (PC doesn't have disk drive) and also a Windows 10 rescue USB made from my housemate's laptop.