Power Cycling, Rebooting Problem - - Power Supply????

I've got an Asus A7N8X-Deluxe that has recently run into a problem
where it will not power off. It just sticks in a constant cycle of
repowering, even before any of the post information is visible. The
only way to turn it off is to turn off the power supply at the rear of
the machine. Could this be a power supply failing.
Any input is much appreciated.
Thanks.

 

Anyway to try another power supply? Thats what I would do first off.

 

Only way to answer that question is to start by measuring power and
signal wire voltages between power supply and power supply controller.
First 3.5 digit multimeter measurement is on purple wire from power
supply to motherboard. This voltage must be more than 4.87 volts.
Next is to monitor green and gray wires. As green goes below 0.8
volts, then gray should rise up above 2.4 volts within seconds. Again,
the numbers would tell us more.

Also important information is voltage across power switch (or where
it connects to motherboard). This voltage should remain well above 2.4
volts.

Numbers will provide sufficient information so that responders can
either identify the problem or begin isolating the problem down to a
single suspect. Currently a list of suspects for your problem is long.