In the last few days my PC has refused to start.

It's initial behaviour was to repeatedly try to power on until I hit the power switch on the power supply.

It now exhibits one of two behaviours:

  1. It does nothing at all.
  2. It briefly powers on before shutting down again.

My initial assumption was that:

  1. The case power button was broken.
  2. The power supply had failed.
  3. The motherboard was dead, possibly as a result of 2.

I used the power/reset buttons from another case with exactly the same results which seems to discount 1.

I bought a power supply tester which initially reports and passes a value of 5.3V on the +5VSB supply rail (I assume it's rounding up) which then jumps to 5.4V and sets the tester beeping.

So the question is would this voltage prevent the PC from starting and is likely to have caused permanent damage to the motherboard?


Based on buying a new PSU and my system now working the answer seems to be yes even a small step outside of the accepted voltage range (+/-5% for the +5VSB rail) will prevent the PC from starting and no it hasn't caused any damage.

In addition a friend provided the following information:

The power-on circuitry in the PSU has various protections built-in for things like overcurrent and shorts.

Usually the PSU refuses to turn on if these kick in.

  • 1
    Take a look here for voltage tolerances. – AndrejaKo Nov 8 '10 at 21:36

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