PowerUp Issues

Issue with amd k8v motherboard machine.
400 watt power supply
4 drives
2 sata
2 ide
2 cdroms
3 fans total

Machine is about 3- 5 years old....
Trying to see whether the issue I'm having with power is the motherboard or the powersupply.
I'm thinking its the motherboard.
Scenario....
Over time the power button became less and less reliable within the last several months. Meaning I would have to press it multiple times for the box to power up.
Now its at the point now where the power button does not boot up the machine.
The machine will power on by itself after a period of time.
I opened the box up and took a look.
The motherboard will show that it has power(green light) but the fans will not rev up nor do the hard drives.
When I hit the power switch next to the power supply to off the fan spins for a second then stops.
Turn on the power switch next to the power supply green light comes on for the motherboard but that's it no fans no hard drive activity. Turn off power switch cpu fan revs for a second and dies...
What do you think guys?

I press the power button on the front of the box no reaction
Antec case.
built the system in 2003/2004
I can give that a try.
The system was up and running and just went totally dead.
Any other suggestions