SN85G4 green LED on but no power

My Pc was on all night but it just stop working. Trying to start but when pressing the power button nothing happens. On the motherboard a green LED is on which switches off if I hold down the power button for some seconds.

If I press the power button again the green light comes on and nothing happens. No fans start or anything working.

Any ideas?

Please help.

Has the ATX12 lead come loose (the 4 pin ATX lead under from the PSU that plugs into the front right of the board)?

Failing that try the usual CMOS reset (jumper switched for a few mins whist unplugged) and report back.