Member Avatar for dwizzle40

I have someone who asked me to look at a machine that won't turn on. I opened the case and the motherboard light is on yet nothing happens when the power button is pressed. I mean nothing happens, no fans, no lights, nothing. I have taken the power supply out and put in a know good psu with the same result; nothing happens. I was told that the owner of the machine was gone over the weekend and when they came back they weren't able to turn it on. So I am unable to find out if weather might have been a factor. If anyone has an idea that would be great.

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Summary and focused triage (adds to question). The OP notes the motherboard LED is lit but pressing the case power button produces no fans, no POST, and a known-good PSU gives the same result. That pattern usually means the board is in standby (+5VSB present) but never sees a proper power‑on signal or the motherboard power-switch circuitry has failed. and raised RAM/CPU and CMOS ideas; those are reasonable later steps but won’t usually give a totally dead system where only the standby LED is on. Try these targeted checks first to isolate the fault.

  • With mains unplugged, remove the case front-panel power‑switch connector from the motherboard. Reconnect mains and briefly short the two power‑switch pins on the motherboard header (momentary contact) to attempt a power-on. If the board powers, the case switch/wiring is bad.
  • If that does nothing, move the board outside the case (on cardboard), connect only CPU + cooler, one stick of RAM, the ATX 24/20‑pin and the 4‑pin CPU power plug, and a speaker. Then try the same short-on‑header test. This eliminates a chassis short and unnecessary peripherals.
  • Check for +5V standby on the PSU/motherboard with a multimeter (only if comfortable). If +5VSB is present but the PSU never turns on when the power pins are shorted, the PSU is suspect; if PSU starts externally but not when the board requests power, the motherboard’s power‑control stage is likely dead.
  • Visually inspect the board and PSU for bulging/leaking capacitors, burn marks, or a blown component. Listen for any faint beeps from a connected system speaker.

Safety/caution: avoid touching live circuits, use ESD precautions, and don’t short pins beyond a quick moment. If bench tests rule out the switch and PSU, the most practical next step is replacement or board-level repair—motherboard power‑stage failures are common and often not worth component-level repair on older Dimension systems.

Member Avatar for romeyng

i'd hate to jump to saying that the board's dead...cus i myself i had that problem with a similiar model....but u can try diff ram modules if u didnt already do so...and also swap the processor...

Member Avatar for dwizzle40

I wouldn't think that would make nothing work, even if the processor was dead you would get something to turn on; fan, light something. The only thing that seems to be lit is the light on the motherboard by the CMOS battery.

Member Avatar for romeyng

thats true....BIOS got corrupted maybe??? thats going out on a limb.....start digging a hole....

Member Avatar for JimPivonka

If you can find the necessary tools and procedures I've seen it recommended in similar cases that you flash the BIOS and reset the CMOS - probably put in a new CMOS coin battery.

Now flashing the BIOS implies that you have a floppy drive and that it works when the machine is powered on. Sometimes CMOS settings do not start the floppy at power on - so resetting CMOS may come both before and after BIOS flashing. Good luck.

Member Avatar for JimPivonka

I've recently seen a case where an add on graphics card in the AGP slot was "lost" to the system during an upgrade, when the CMOS was altered. The result was that no video signal could be propagated, and boot could not be completed.

The cure was to remove the add on AGP graphics card and plug the monitor into the default on-board graphics processor. This permitted registration of the upgraded HDD and memory. The AGP graphics will have to be reinstalled.

Member Avatar for dwizzle40

Just tested the power supply and it is working properly, the motherboard you suppose could be the problem? Light on the motherboard is on when plugged in but nothing else works.

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