Lately my PC has occasionally been showing a black screen after the BIOS screen on startup that requires me to hold down the power button to cancel. When It did it the other day I left it half an hour and checking Windows event log afterwards there were entries from all through that period suggested windows had launched and later restarted and resumed from sleep. The first startup also had a message that it had improperly shut down despite there being no sign of that.
I'm also seeing occasional graphical corruption. It was only in the web browser (vivaldi) so I'd written it off as a simple rendering issue but I've now seen a couple of flashes on shut down.
These problems are intermittant happening only once every day or two.
The computer is a B250 Mini-ITX motherboard with a PCI-E Riser and RX 460 4GB. No issues show up during heavy gaming?
Can anyone know what it might be or can suggest any tests that could pin it down or cause problems to show up more reliably?