computer powers off suddenly but mobo led lights still on sort of froz

When I hit the power switch it gives me all four phase led lights on the motherboard, all the fans are going, but it seems to be stuck in that position, no boot-up sequence, no signal to the monitor, nothing.

If I hit the reset power button, sometimes it does nothing and continues to be stuck and I have to turn the power switch on the PSU off. Occasionally when I hit the reset power button, it will go through the boot sequence and boot all the way to Windows Vista. However, after a few seconds the monitor goes blank, as in no signal to the monitor, and I am back to the place where I started, before hitting the reset power button (4 leds on the Mobo phase 1-4 all lit up, and the two indicator leds dark.)

This time (after it has turned itself off) when I hit the reset button nothing happens, when I hold down the power button nothing happens, I have to turn off the power to the PSU again. When I do this and wait thirty seconds or so, then power on and press the reset button it boots up but then turns off again in another minute or so.

What is going on here? It seems to me to be some sort of power problem where the board is powering down automatically for some reason. Could it be overheating and powering down because of that?

I have tried...
1) taking out a stick of a ram and trying each ram individually in various slots, same thing happens.
2) I replaced the power supply with this much more powerful one and it is the same.

I tried everything else on the checklist to try but to no avail.
3) breadboarding the system with no dvd/blu-ray drive hooked up, just hard drive and ram, same thing happens.

Also, when I installed the new power supply and powerd it up I did here some beeps, I wasn't really paying attention to them at the time, but now I cannot get it to repeat the beeps at all as in no beeps at start up. Any ideas? Thanks!

BIOSTAR TForce TA790GX A3+ AM3 AMD 790GX HDMI ATX AMD Motherboard
AMD Phenom II X2 550 black 3.1ghz dual core processor
Heat sink is stock that came with processor from AMD
G.SKILL 4GB (2 x 2GB) 240-Pin DDR3 SDRAM DDR3 1333 (PC3 10600)
SAPPHIRE Vapor-X 100269VXLE Radeon HD 4890 1GB 256-bit GDDR5
SAMSUNG TOC T260HD Rose Black 25.5" 1080p monitor
Windows vista home premium 64bit edition
Western Digital Caviar Black WD6401AALS 640GB 7200 RPM SATA 3.0Gb/s 3.5" Internal Hard Drive
hec Prime Black 0.8mm SECC Steel ATX Mid Tower Black Computer Case has one 120mm case fan
LITE-ON Black 4X Blu-ray Reader SATA Model iHOS104
Sony Optiarc 24X DVD/CD Rewritable Drive Black SATA Model AD-7240S-0B
6 answers Last reply
More about computer powers suddenly mobo lights sort froz
  1. Build outside the case with only processor, power and beeper. Listen for beeps. Keep adding components. Listen for beeps and look for video.
  2. I will try that, but I don't have a beeper right trying to get my hands on one.

    I did try each stick of ram individually in the first ram slot, second ram slot, third ram slot and still get the same problem with both sticks of ram.

    Two questions about that...It seems to me unlikely that both of my sticks of ram would be bad, is this common? Also, it will boot all the way to windows and then shut down again, is it possible that it would boot all the way to windows with bad ram and then suddenly shut down?

    Thanks for the help! I will continue trouble shooting, I'm determined to figure this out.
  3. Internal PC Mini Speaker

    Did you set the memory voltage?
    Could be a defective power supply.
    Check voltages in the bios for +-10%. Replace the Power Supply if over 10%.
    Check CPU and other temperatures in the bios.
  4. Boot problems:

    To check PSU:
    Try to verify (as well as you can) that the PSU works. If you have a multimeter, you can do a rough checkout of a PSU using the "paper clip trick". You plug the bare PSU into the wall. Insert a paper clip into the green wire pin and one of the black wire pins beside it. That's how the case power switch works. It applies a ground to the green wire. Turn on the PSU and the fan should spin up. If it doesn't, the PSU is dead. If you have a multimeter, you can check all the outputs. Yellow wires should be 12 volts, red 5 volts, orange 3.3 volts, blue wire -12 volts, purple wire is the 5 volt standby.

    The gray wire is really important. It sends a control signal called something like "PowerOK" from the PSU to the motherboard. It should go from 0 volts to about 5 volts within a half second of pressing the case power switch. If you do not have this signal, your computer will not boot. The tolerances should be +/- 5%. If not, the PSU is bad.

    Unfortunately (yes, there's a "gotcha"), passing all the above does not mean that the PSU is good. It's not being tested under any kind of load. But if the fan doesn't turn on, the PSU is dead.
  5. evongugg said:
    Internal PC Mini Speaker

    Did you set the memory voltage?
    Could be a defective power supply.
    Check voltages in the bios for +-10%. Replace the Power Supply if over 10%.
    Check CPU and other temperatures in the bios.

    Hi. I may have similar problem as james. Just curious, when you say "Check voltages in the bios for +-10%. Replace the Power Supply if over 10%.", what part of the BIOS should we look at? Or is this something to be still computed?
  6. If you can get into BIOS, the voltages are generally in something like "PC Health".
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