Computer does not start sometimes!

[gselvam]

I am facing a strange power issue with my computer.
The problem is, whenever I press the
button, the computer is not switching on. It remains like a dead
system. But after few hours, it boots by itself and works normally
until I shut down. When I shut down my computer, it shuts down
completely but the cpu fan keeps rotating and the power light remains
on, the system does not go to complete off state. I forcefully switch
off CPU and the story continues like when I press it does not boot,
after some hrs........!! Technical support at the manufacturer told me
to change powersupply, but it didnt help. then they asked me to change
the button which controls on/offf. It also didnt help... Now I am
really confused with what is going on... since my system works without
hanging even for several days when it got booted, I could not doubt on
motherboard also. Could anybody give any suggestions? I would
appreciate of any help as it is troubling me a lot.

Thanks

 

[Lez Pawl]

I am facing a strange power issue with my computer.
The problem is, whenever I press the
button, the computer is not switching on. It remains like a dead
system. But after few hours, it boots by itself and works normally
until I shut down. When I shut down my computer, it shuts down
completely but the cpu fan keeps rotating and the power light remains
on, the system does not go to complete off state. I forcefully switch
off CPU and the story continues like when I press it does not boot,
after some hrs........!! Technical support at the manufacturer told me
to change powersupply, but it didnt help. then they asked me to change
the button which controls on/offf. It also didnt help... Now I am
really confused with what is going on... since my system works without
hanging even for several days when it got booted, I could not doubt on
motherboard also. Could anybody give any suggestions? I would
appreciate of any help as it is troubling me a lot.

Thanks

I'll suggest its the main 20 pin connector on the MoBo.

Probably once per month I have to disconnect and reconnect it cos the comp
will not fire up.

 

[sbb78247]

I'll suggest its the main 20 pin connector on the MoBo.

Probably once per month I have to disconnect and reconnect it cos the
comp will not fire up.

maybe you should buy a new one?

 

[Rod Speed]

I am facing a strange power issue with my computer.
The problem is, whenever I press the
button, the computer is not switching on. It remains like a dead
system. But after few hours, it boots by itself and works normally
until I shut down. When I shut down my computer, it shuts down
completely but the cpu fan keeps rotating and the power light remains
on, the system does not go to complete off state. I forcefully switch
off CPU and the story continues like when I press it does not boot,
after some hrs........!! Technical support at the manufacturer told me
to change powersupply, but it didnt help. then they asked me to change
the button which controls on/offf. It also didnt help... Now I am really
confused with what is going on... since my system works without hanging
even for several days when it got booted, I could not doubt on motherboard also.

It likely is a bad motherboard since a replacement power supply made no difference.

It cant be the switch, that wont produce that delayed boot effect.

 

[Paul]

I am facing a strange power issue with my computer.
The problem is, whenever I press the
button, the computer is not switching on. It remains like a dead
system. But after few hours, it boots by itself and works normally
until I shut down. When I shut down my computer, it shuts down
completely but the cpu fan keeps rotating and the power light remains
on, the system does not go to complete off state. I forcefully switch
off CPU and the story continues like when I press it does not boot,
after some hrs........!! Technical support at the manufacturer told me
to change powersupply, but it didnt help. then they asked me to change
the button which controls on/offf. It also didnt help... Now I am
really confused with what is going on... since my system works without
hanging even for several days when it got booted, I could not doubt on
motherboard also. Could anybody give any suggestions? I would
appreciate of any help as it is troubling me a lot.

Thanks

The problem is the interface between the motherboard and the
power supply.

The motherboard has an open collector signal which brings
the PS_ON# signal to ground level, when the motherboard wants
the power supply in the ON state. The motherboard leaves
the PS_ON# signal in a floating state, when it wants the
motherboard off. It is the responsibility of the power
supply, to pull the PS_ON# signal up to +5V, when the
motherboard is not pulling it down.

PS_ON# - zero volts is "ON" (see somewhere between 0 and 1V perhaps)
PS_ON# - 5.0 volts is "OFF" (see somewhere between 2V and 5V perhaps)
(Ideally, you really want the voltages to be 0V and 5V, but if
things aren't healthy, then the above range of values might be seen.)

What you can do, is probe the PS_ON# signal on the main
ATX cable, with a voltmeter. If you shutdown the computer,
and PS_ON# is still close to 0 volts (like 1V or a little
lower), then the motherboard is still telling the power
supply to run. If you attempt to turn on the computer,
and probing PS_ON# shows a voltage between say 2.0V and
5V, then the motherboard still isn't sending the command
to turn on the supply.

So the driver on the motherboard could be bad.

Or, an alternative theory, is your motherboard is
dragging down the +5VSB supply. That is the supervisor
voltage for the power supply, and the standby voltage
for the motherboard. If +5VSB is overloaded, that can
stop the thing from starting.

If you have replaced the power supply, the next logical
thing to replace, is the motherboard. The above probing
nonsense, is only if you are curious as to what is
going on.

Paul