Previously functioning computer won't boot past mobo screen


I built a pc in December of 09 and it's been running perfectly. Then, last night, it started turning itself off in the middle of watching a movie or even just after sitting there doing next to nothing. (This happened twice in probably three hours of use.)

This morning, when I went to turn it on, it booted to show the gigabyte mobo screen, and then immediately afterward went to a black screen with a flashing line in the top left corner (like when you're typing). When I went to show my husband what was happening, it did the same thing, but this time it lasted a bit longer before stopping after the second boot screen.

Last Saturday I added 4 gb of ram to the PC and downloaded AMD overdrive so I could OC it. I never actually overclocked, though, because my core temp was already at 46C and when I started running autoclock it jumped to 75C within a few seconds. I pulled the plug on that as soon as I noticed that the cores were so high. However, now I'm thinking I might have fried my CPU.

So if anyone has any ideas (preferably less expensive ideas), please let me know!

Here's my system:

Gigabyte MA790X-UD4P
AMD Phenom II quad core 3.4GHz
8 gb DDR2
Western Digital 1 TB 7200 rpm HDD
Windows 7 64-bit

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  1. Best answer
    I would re-apply the thermal paste to the CPU and re-install the heatsink and fan on it. The CPUs have a thermal "safety" that prevents heat damage. But, there is always a chance you might have nudged the heatsink during the RAM installation. Thermal paste is inexpensive and this would be the first step I would take.
    Another easy check would be to remove the added RAM sticks and see if it boots from there. If it does, run Memtest on the new RAM, it could be that one of them is bad.
  2. Work systematically 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, 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.
  3. Best answer selected by trogdorita.
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