Bad Power Supply Franck.http://h18000.www1.hp.com/products/quickspecs/10692_div/10692_div.html
Power Supply has a weak voltage power rail.
(Or more than one.
There are three main voltage power rails.
1) The 3.3 Volt power rail
2) The 5 Volt power rail
3) The 12 Volt power rail)
The Power Supply has enough power to light the Power On LED, and 'electricity' LED, but Not enough power to turn the Processor on.
A) If ALL of the LED lights were on at once they would use less than 1 Watt of power.
B) EACH fan uses 2 to 3 Watts.
C) A typical Processor can use 51 to 125 Watts of power.
(Less for older processors such as an Intel Pentium III)
An Intel Pentium III model 1266S processor, (Tualatin Core) can use up to 30.4 Watts.http://en.wikipedia.org/wiki/List_of_Intel_Pentium_III_microprocessors#.22Tualatin.22_.28130_nm.29
Why is the Power Supply bad?
Two main causes of computer failure;
1) The computer is dirty inside to include the Power Supply.
Power unplugged from computer, Anti-Static Precautions observed, a can of compressed air for computers is used to clean the inside of the computer, and the Power Supply. (The best you can through the Power Supply's case ventilation holes)
2) Bad Power Supply.
Some of the components inside a computer power supply are Electrolytic Capacitors.
(Radial Aluminum Electrolytic Capacitors to be specific)
Electrolytic Capacitors break down after time.
The Power Supply used in a personal computer is an SMPS.
Switched-Mode Power Supply,http://en.wikipedia.org/wiki/Switched-mode_power_supply
Electrolytic Capacitors are used in the Input Stage, and Output Stage.
They Filter the incoming AC electricity, and the outgoing DC electricity.
In the above link click on the photo of an exposed SMPS to the upper right of the page.
The letter B is on top of one of the two large Electrolytic Capacitors used in the Input Stage.
The letter E is in the middle of surrounding smaller Electrolytic Capacitors used in the Output Stage.
Basic construction of a Radial Aluminum Electrolytic Capacitor, is a small aluminum can with two strips of aluminum foil, and a strip of paper soaked with Electrolytic Paste, installed inside.
There are three strips.
A) One strip is the Conducting strip.
A strip of aluminum foil.
B) One strip is a Non-Conducting strip. A strip of aluminum foil with a non-conducting medium applied to it.
C) A paper strip which is soaked with Electrolytic Paste.
The paper strip is laid in-between the two metal strips, and all three are rolled up tightly, then installed in the aluminum can case.
The Conducting strip has a lead (Think wire) attached to it, and it is the Positive connection.
The Non-Conducting strip has a lead to it also, and it is the Negative connection.
These two leads come out of the bottom of the capacitor through a Bung.
(Flat synthetic rubber disk)
The top of the 'can' has a flat metal aluminum disk. This disk is etched with a pattern part way into the disk's surface.
The pattern is usually a K or X.
When the Electrolytic Paste breaks down it forms a gas. Hydrogen Gas.
The gas expands, and pushes the paste out of the capacitor.
(Though the cracked open K or X on top, and/or pushes one side of the Bung out of the bottom)
So much paste loss, and the capacitor operates in a weakened state.
Too much paste loss, and the capacitor fails.
Electrolytic Capacitors are the weakest link in an SMPS.
This is Not an invite to try to repair the SMPS in your computer.
The best solution is to replace it.
This is from a quick search,http://codemicro.com/store/product/207728001/Refurbished
The power supply used in the Compaq Proliant DL320 server computer, is not an average one you can buy anywhere.
The above however is just from a quick search. You may find a better price. (Just make sure it's a reliable source, IMHO)
HP Support > Compaq Proliant DL320 > Service Manual, (Service Guide is a Service Manual),http://h20000.www2.hp.com/bizsupport/TechSupport/DocumentIndex.jsp?contentType=SupportManual&lang=en&cc=us&docIndexId=64180&taskId=101&prodTypeId=15351&prodSeriesId=427542#2
Click on the file - HP Proliant DL320s Server Maintenance and Service Guide
Shows you how to open the computer, and change out the power supply.
Computer unplugged from power, observe Anti-Static Precautions.
Your body carries Static electricity.
Static will fry out (Short Circuit) the delicate hardware components inside a computer.
Relieve your body of Static BEFORE working on your computer.
Computer unplugged from power, computer case open, TOUCH the metal frame of the open computer case.
IF you leave your computer in the middle of working on it, be SURE to touch the metal frame again upon your return ]
For additional questions please post in a Comment.