Computer turning off after booting up?

Well I came back to my computerafter eating dinner and watching a movie. i booted my computer back up and i was able to login to msn and chat for a minute before it turned off. then i turned it on again and it lasted until i had barely even logged in. I assumed it was a virus, so I tried logging into safe mode, halfway into loading safemode, it turned off. Then it instantly turned off if I turned it on, we messed with the heatsink/fan and it lasted around 20 minutes then turned off. After that it instantly turned off when turned on. We unclipped it and messed with it and it lasted 5 minutes. We applied thermal paste and then it lasted around 10, then instantly started turning off again. Could someone give me some advice?

Also, we checked for burnt out caps and there doesnt seem to be any and the temperature was steady at around 25 degree celsius. We just texted a professional to see if he can help us, but I would prefer if we could fix it ourselves.

Thank you for your time and assistance.
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  1. Sounds like its more a power supply issue. When you turn it on does the PSU fan spin up? If not its got a bad fan and probably overheating.

    If the fan spins but it continues to just turn off then something inside the PSU itself blew out. I would try a test PSU, but it is probably the issue. I replace a lot of PSUs at work that do the same thing.
  2. Have you checked temperatures? Load coretemp or somethinglike that thencrank it up and watch the temps as it is running.
  3. usually hardware problems reacts this way. if the gcard and mobo has the problem, your cpu is turned on, has lights has the fans rolling and everything except your monitor, it is shut off, but the cpu will continue and will not power off. memory problems will cause restarting or hanging, not turning off. but cpu turning off if that is your case your psu is causing it.
  4. Probably, but not necessarily, the PSU.

    System specs?

    The following is an expansion of my troubleshooting tips in the breadboarding link in the "Cannot boot" thread.

    I have tested the following beep patterns on Gigabyte, eVGA, and ECS motherboards. Other BIOS' may be different, but they all use a single short beep for a successful POST.

    Breadboard - that will help isolate any kind of case problem you might have.

    Breadboard with just motherboard, CPU & HSF, case speaker, and PSU.

    Make sure you plug the CPU power cable in. The system will not boot without it.

    I always breadboard a new build. It takes only a few minutes, and you know you are putting good parts in the case once you are finished.

    You can turn on the PC by momentarily shorting the two pins that the case power switch goes to. You should hear a series of long, single beeps indicating memory problems. Silence indicates a problem with (in most likely order) the PSU, motherboard, or CPU. Remember, at this time, you do not have a graphics card installed so the load on your PSU will be reduced.

    If no beeps:
    Running fans and drives and motherboard LED's do not necessarily indicate a good PSU. In the absence of a single short beep, they also do not indicate that the system is booting.

    At this point, you can sort of check the PSU. Try to borrow a known good PSU of around 550 - 600 watts. That will power just about any system with a single GPU. If you cannot do that, use a DMM to measure the voltages. Measure between the colored wires and either chassis ground or the black wires. Yellow wires should be 12 volts. Red wires: +5 volts, orange wires: +3.3 volts, blue wire : -12 volts, violet wire: 5 volts always on. Tolerances are +/- 5% except for the -12 volts which is +/- 10%.

    The gray wire is really important. It should go from 0 to +5 volts when you turn the PSU on with the case switch. CPU needs this signal to boot.

    You can turn on the PSU by completely disconnecting the PSU and using a paperclip or jumper wire to short the green wire to one of the neighboring black wires.

    A way that might be easier is to use the main power plug. Working from the back of the plug where the wires come out, use a bare paperclip to short between the green wire and one of the neighboring black wires. That will do the same thing with an installed PSU. It is also an easy way to bypass a questionable case power switch.

    This checks the PSU under no load conditions, so it is not completely reliable. But if it can not pass this, it is dead. Then repeat the checks with the PSU plugged into the computer to put a load on the PSU.

    If the system beeps:
    If it looks like the PSU is good, install a memory stick. Boot. Beep pattern should change to one long and several short beeps indicating a missing graphics card.

    Silence, long single beeps, or series of short beeps indicate a problem with the memory. If you get short beeps verify that the memory is in the appropriate motherboard slots.

    Insert the video card and connect any necessary PCIe power connectors. Boot. At this point, the system should POST successfully (a single short beep). Notice that you do not need keyboard, mouse, monitor, or drives to successfully POST.
    At this point, if the system doesn't work, it's either the video card or an inadequate PSU. Or rarely - the motherboard's PCIe interface.

    Now start connecting the rest of the devices starting with the monitor, then keyboard and mouse, then the rest of the devices, testing after each step. It's possible that you can pass the POST with a defective video card. The POST routines can only check the video interface. It cannot check the internal parts of the video card.
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