Power supply unit is working but no power to computer

Computer was working and stopped overnight. I believe the Power Supply Unit is still working (green light on the PSU is on and there is a brief flicker of light on the computer light bar when I do the unplug/hold power button for 10 seconds routine) but nothing happening with the power button/computer otherwise (i.e., no lights/whirring sounds/clicks to indicate anything is on). I have read this might be a motherboard issue or perhaps the connecting ribbon from the power supply to the computer. Any ideas/suggestions/answers?