Computer shutting down

My system over the past couple of months has been getting slow. In the past week it has gotten much worse. Then it started shutting down when loading my settings. Now it starts to boot gets to log on screen and shuts down. I have an ASRock mb 3.3 GHz duel core,Geforce Video card and 2G memory, PS is ATX-PSIV-4502
After some testing --unplugging drives/video card to see if they were the fault--nothing changed. Even if I unplug all drives,video card it still shuts down. I unplugged the 12v ATX plug and it does not shut down--plug it back in and--shut down.
What could be my problem? Is it MB or PS? Any help would be nice.
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  1. Work through our standard checklist and troubleshooting thread:
    I mean work through, not just read over it. We spent a lot of time on this. It should find most of the problems.

    If not, continue.

    I have tested the following beep patterns on Gigabyte, eVGA, and ECS motherboards. Other BIOS' may be different.

    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 or long single beeps indicate a problem with the memory.

    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.
  2. smokey_55 said:

    What could be my problem? Is it MB or PS?

    Based on your description, probably not. It sounds like it is something that has been developing over time. Have you tried booting into safe mode? My first guess would probably be corrupted drivers, possibly do to the hard drive going bad and there being increasing numbers of bad sectors. I would install the Recovery Console (if it's not already installed). Then boot into the Recovery Console and run chkdsk /R for that drive and let it scan for and repair bad sectors. Then if possible, use a recent restore point or "last known good configuration". if the chkdsk found errors, you probably want to get a new HD ASAP.

    if the CPU was overheating, it would cause shutdowns, but they wouldn't be happening at one particular spot. It would vary more. But you can easily check the CPU temp in the BIOS to be sure.

    If it were the power supply, it would also be more random, especially since you already tried unplugging things.

    Bad memory would more likely crash the computer rather than shutting it down, but you could always download and run memtest from a bootable CD or floppy, if you want to test it.
  3. Capacitor aging may have rendered what looks like a cheap PSU even less capable than it was when new.
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