Member Avatar for Phunkizm

I have a Sony Vaio RB40 and the cpu overheated. I turned it off and waited overnight to turn it on. When I plug in the power cord the light on the psu and the mobo blinks and the pc will not power up. If I unplug the 24 pin cable from the mobo then plug in the power cord to the psu the light on the psu stays solid. Do I have a bad mobo? Thanks for any help!

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Given what reported and the checks suggested, the behaviour you describe — PSU LED steady with the 24‑pin unplugged, but the PSU and motherboard LEDs start blinking as soon as the main connector is attached — usually means the PSU is going into protection immediately when it sees the board load. That narrows the problem to a short or heavy draw on the motherboard side (power-delivery circuitry, a short to chassis, or a damaged CPU/VRM) rather than a PSU that simply won’t turn on.

Next diagnostic steps to try (in order, lowest cost/effort first):

  • Bench the board outside the case on a non-conductive surface (cardboard or antistatic mat). Connect only the ATX 24‑pin and the CPU 4‑pin/8‑pin, install the CPU/heatsink, leave RAM and drives disconnected, then try to start by shorting the front-panel power pins. If the PSU still cycles, the fault is on the board/CPU; if it stays on, suspect a short to the case or a bad standoff.
  • Visually inspect the CPU area and VRM: look for bulging/leaking capacitors, scorched components, melted connector plastic or discoloured PCB traces. Smell for burnt odours. Check the 24‑pin and CPU power connector pins for melting or corrosion.
  • Verify the PSU under load with a known‑good PSU or a proper PSU tester (paperclip tests only prove the fan runs; they don’t replicate a real motherboard load). A multimeter can confirm rail voltages but only if you are comfortable and careful with mains electricity.

If the board still forces the PSU into protect mode with a known‑good PSU on a bench, the motherboard or CPU is almost certainly failed. At that point, component‑level repair or board replacement is the choice — keep in mind many OEM systems use proprietary boards, so compare repair cost versus replacement. If replacing parts, also replace thermal paste and correct the cooling that caused the original overheat.

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Member Avatar for finito

Hmm, to test the mobo take out the Ram DIMMS.

You should hear a pattern of beeps.

When you turn it on do you or did you hear a Siren?

If you don't hear the pattern then there is a fault with your motherboard or Processor.

P.S. it would be wise to remove everything. Pci CArds, USB devices, Leave only the Bare Minimum.

CPU w/heatsink and PSU. (No Ram no Graphics card unless it's built in).
This is to test whether your mobo works.

If you hear the Beep Pattern. Turn of your PC.

Member Avatar for finito

After you have established the Beep Pattern Exists. Re-insert your Ram.

You have to fix the issue of overheating. Unmount your Heatsink and readjust it it should be very secure. you should be able to lift your motherboard with the heatsink without any wobble. (Ofcourse don't try this if the motherboard is secured to the case)

Now add your graphics card and test if you get the screen.

Now add your components one by one and booting to see if it worked. This is to test if all your components work.

Tell me how it went.

Member Avatar for Phunkizm

I unplugged everything from the mobo except for the cpu. It is doing the same thing it did before. As soon as I plug the psu into the mobo and insert the power cord I get a steady blinking green light on the psu and mobo. It will not power up, only green lights blinking. I assume if it is the cpu or the mobo I could probably just buy a cheap new tower for around the same price....

Member Avatar for finito

So no beeps huh. Yeah then, It could be processor or the motherboard.

You seem to know your options, please mark as solved if solved.

Member Avatar for Phunkizm

Yeah, no beeps or siren. All I get is the blinking lights. Thanks for your help!

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