Should rear fan run all of the time or only when needed?

buy a replacement power supply fan
or
buy a replacement power supply - dearer option but power supply may be faulty if fan is not running and you fix two problems however be careful with AC input voltage that it matched the power point voltage. or smoke and broken power supply ! take old power supply to computer shop to ensure correct power supply is purchased.
or
if it is the cpu fan
buy a replacement cpu fan and thermal paste.

Possible cheaper options if fan choked full of dust
get a can of compressed air and blow the dust out of the power supply and cpu fans outside your dwelling not inside your your office/ home.
Power supply fan may need a drop of machine oil if noisy or its bearings are worn out..

It appears you have a faulty CPU fan and it is causing the CPU to overheat and shut down.
I suggest you replace the CPU fan. remove any dust from the heatsink and put new heatsink compound on the CPU/heatsink.

Unplug everything inside the computer, except the motherboard and the front panel power on switch. Power up the computer. If the PS fan continues to run, (power supply doesn't shut down)and the CPU fan runs, then power off the unit and reinstall each device, one at a time, turn the power supply on after each device is installed (and off, before installing the next device).
You can not easily start the power supply if it is not connected to the cpu motherboard.
If the power supply shuts down with only the motherboard attached, then you will need either another power supply, to test the MB, or another MB to test the power supply.
R

Had the same problem myself a few weeks ago.

1) Check the cpu and heatsink are clear of dust and rubbish. If CPU's overheat, the PC can also shut down.

2) If so, then yes it could well be your PSU. Give it a good blow through/clean.
If that doesn't work then it needs to be tested, you can get small testers or go to a repair shop and ask them to test it. But make sure the test is run for about 30 minutes. I had mine tested, paid money, test came out good, but it wasn't run for long enough. Tested again it failed after 15 mins.

3) If you want to avoid that route first, take out the psu, dismantle it and check the printed circuit board, if you see what looks like a yellow fluid stain under some capacitors, one of them has failed. You need to replace it. But as a replacement CPU shouldn't be too much, I wouldn't go to too much trouble, unless I wanted to have the fun of repairing it.

Very well could be overheating or powersupply problem. Most Definately Hardware related. You can try opening up the case and blowing air into it from compressor. (Make sure to do this outside away from clean items). Also, check CPU fan and heatsink to make sure fairly clean. CPU fan may also be old and need to be replaced. Don't put case back on and try again. Look at CPU fan to see if moving (or struggling). If computer stays on longer then CPU fan most likely the problem. If off in same time as before then most likely the main power supply problem, in which case the only way to check this is to replace the power supply. Hope this helps, Best Regards,

I agree...sounds like a power supply problem. Typically a bad power supply will not damage the motherboard. It should still be functional.

you need do some thing follow:
1) clean the cpu fan and sink(around there dirdy)
2) check the cpu fan is running and stop ok when power on if running go next
3) check the cpu fan, is there any running and stop then see it run again before the laptop freezen?
4) if the fan not running again before freezen that your fan control circuit out of work on the motherboard need to repair
5) if the fan running control ok that the fan can run and stop and run again. you have to add a EXT cooling base under the laptop
hope to help you solve it

Hi Gene,

If you've installed the cpu and hooked the fan to the power supply plug, which is just left of the cpu mount, then the board if connected to the power supply cables, it should start up. Regardless of the front switches. However, you probably don't want to start plugging in the power cord until you have all of your components in place and ready to close up the case. First you can create a shock by just touching the board and that can damage the board. (I speak from my own experience :-( .

But once you get the power switch plugged into the board that should take over turning the rear power supply on and off (Including the cpu fan)

Good Luck and don't forget to leave a rating, based on my solution.

Thanks Mark

Which fan are you referring to? As far as I know the fan in the power supply runs at the same speed at all times. So if that is the fan you are hearing it may indicate that the power supply is failing. The power supply may be over heating and shutting down. I would try a different power supply if you can get your hands on one.

when you disconnected the battery, the CPU (computer) modulke got de-programmed. disconnect the negative cable from the battery. Wait a minute then reconnect. you may have to do this several times.The purpose is to reprogram the computer.