I built a Wintel desktop PC in 2014.

Today I suddenly have a boot problem:
On cold boot the fans and lights come on for 1 second, then switch off for another 3 seconds, and this cycle repeats indefinitely until I force it to close down.
Nothing shows on the monitor.

I have re-inserted the RAM, checked the mobo for swollen capacitors, and disconnected all drives except the system drive. This makes no difference.

I woulds like to repair this unit despite its age, as most components were pretty high-spec in their day, and it worked very well until it died.

The system:

AsRock Z97 Extreme 6 mobo (chosen because it has 10 SATA3 ports)
Intel i5 CPU Gen5, water cooled
4 x 4GB DDR3 RAM
OCZ REVODRIVE 350 SSD 480GB (system drive)
6 x 4T WD Red HDDs (not in RAID array)
Asus STRIX-GTX970 graphics card
Corsair RM1000 1000 Watt modular PSU (overkill !)

All in a large well-ventilated case with 6 fans - never runs hot.

With a 32" BENQ 4k monitor

Is this likely to be a power supply problem?

All contributions gratefully received.  🙃