I've lost count of case mounting issues. Yes there can be more like that motherboard with a bad manual that had folk putting a HDD LED on the RESET connection. You don't need anything other than the power connections and the power on to test. Here's a video about this.
I've been building PCs for nearly 30 years but this issue has got me puzzled. So there I was transcoding a video and PC just went off. No flash, no bang, just off. Right first thought PSU has died. Got an old PSU and tried that - no joy. Took both PSUs and did the insert paper clip into mains plug to test if they are actually working - both PSUs came on with this test. So has to be motherboard. Bought a new motherboard, inserted CPU, RAM and connected cables, turned on got message "No display". Swapped out graphic card for an old one that doesn't need any power straight from PSU - still no display. Swapped out PSUs - same message. Right has to be CPU. Bought new CPU, installed it on new board, turned on, power light came on, heard CPU fan speeding up and down but still no display. Cleared CMOS tried again - same result, swapped out RAM from another machine, swapped PSUs (again) - same result. Machine sounds like it is trying to start but no display. Moved entire machine to a different power outlet in house - no joy. Tomorrow, out of desperation, a new PSU will arrive. If this don't work I am lost. The whole system will be new. I don't connect HDDs/SSDs when powering on as all I want to see is the POST screen.
What is going on?