This Is Not A
Not That, Then
Everything OK on this machine last night. Came to switch it on this morning: lights come on, fans whirr, but no POST, no signal. Sod!
Fired up my old Windows 98 rig again to do some research. Found a suggestion which might work: disconnect everything (but everything), hold the power button in for thirty seconds and then reconnect just the power. Did that, powered up. BEEP! Good-o!
Of course, then I had to power it off to reconnect everything before firing it up again.
The remedy above seems to reset something in the PSU. I'm on pins now, hoping the damn thing won't start acting up again, and at a weekend as well.