Three main things can cause this.
1) Inside of computer is dirty, as well as the inside of the Power Supply.
Dirt, dust, etc, can cause the cooling components capacity to drop tremendously.
If the Processor overheats, it is turned off. (BIOS turns it off)
This is a Fail Safe feature that is built-in, to keep the Processor from burning up. (Literally)
A non- working Processor fan, or one that works intermittently, or doesn't spin as fast as it's supposed to, will also cause the Processor to overheat.
The major cause of computer failure, is that the computer, (And Power Supply) is dirty inside.
Solution is to have the computer unplugged from power, computer case open, use a can of compressed air for computers, and clean the inside of the computer, PLUS the inside of the Power Supply.
(Read about Anti-Static precautions below, BEFORE you do)
2) Power Supply is bad. Weak voltage power rail, brought about by failing components inside the Power Supply.
Test the Power Supply for voltages.
Computer power supply's, supply three main voltages.
A) 3.3 Volts
B) 5 Volts
C) 12 Volts
[Orange insulated wires are 3.3 Volt.
Red wires are 5 Volt.
Yellow wires are 12 Volt.
ANY Black wire is a Ground wire]
This test can be done with an inexpensive multimeter, or a Power Supply Tester.
The Positive (Red) probe lead of the multimeter, is connected to the power wire to be tested.
The Negative (Black) probe lead is touched to any Ground wire.
The 12 Volt power can be 11 to 13 Volts. Below 11 Volts it's time to replace the Power Supply.
This is one example of an inexpensive, easy to use Power Supply Tester,
http://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=5250576&CatId=5471Or, a compatible, KNOWN to be good power supply, can be substituted, and used for a test unit.
3) Electrolytic Capacitors are failing on the motherboard.
Specifically, the ones used in the motherboard Voltage Regulator Circuit.
One of the jobs the Voltage Regulator Circuit does, is to regulate voltage for the Processor.
A Processor must have a Steady, Clean, supply of voltage, and the voltage MUST be kept within a certain range.
This range, or Tolerance Zone, is VERY small.
Too little voltage the Processor turns off.
(No Processor operating, No computer)
Look for obvious signs of capacitor, (Electrolytic Capacitor) failure.
http://www.capacitorlab.com/visible-failures/index.htm(Takes a couple of seconds before the page fully loads)
This is what happens when Electrolytic Capacitors are failing, in the motherboard Voltage Regulator Circuit,
http://www.youtube.com/watch?v=KN6_-8fYHo0(Starts at 0:04)
Solution is to replace failing, or failed Electrolytic Capacitors, or replace the motherboard.
To summarize:
1) Check to see if the computer is dirty. If so, unplug from power, open the computer case, use a can, or two of compressed air for computers.
2) Visually inspect for bad capacitors.
(BEFORE reaching inside a computer, have the computer unplugged from power. Observe Anti-Static precautions.
Your body carries Static electricity.
Static WILL fry out {Short Circuit} the hardware components inside a computer.
Work on a table. Computer Unplugged from power. Computer case open, TOUCH the metal frame to relieve your body of Static.
SHOULD you get up, walk away, then return, TOUCH the metal frame again)
3) Test the voltages of the power supply, or use a KNOWN to be good, compatible power supply for a test.
NOTE*
The Power Supply may light lights, and spin fans. It may even sound as though the Harddrive is running.
However if the Power Supply has a weak voltage power rail, there won't be enough power to turn the Processor on.
A) All the lights use less than 1 Watt of power.
B) EACH fan uses 2 to 3 Watts.
C) A typical Processor can use anywhere from 51 to 125 Watts. Depends on what Processor it is.
No Processor operating, the Harddrive just sits there, and spins the Platters inside.
There is no Processor to find the boot sector located on the Harddrive.
That's why it sounds like the Harddrive is operating, but in reality it isn't.
Read this to know how a Harddrive is made up, and about the Platters I referenced to above,
http://computer.howstuffworks.com/hard-disk.htm
×