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Product: Compaq Presario S5000NX PC Desktop with XP Pro
Details: After shutting down, the power button causes the CPU fan to try to start and at times will go full blast for a second then returns to vibrate. The full blast does not last long enough for proper boot. This is an intermittent problem in that on one occasion, the machine booted and worked properly after fan started full blast. However, when I put the computer to sleep and woke it up, the computer had the same problem. The drive lights and the power supply lights all work. When the fan vibrates, there is a ticking noise as if it is trying to start and it actually rotates a degree or two then reverses.
The normal startup procedure for this machine is for the CPU fan to come on full blast for maybe 10-sec, boot occurs, then fan slows to a quiet running speed. "Full blast" means a high speed with lots of fan noise. I have replaced the fan and removed heat sink and replaced with new compound. Voltages at the fan red-black wavers around 1-volt when fan doesn't run but on rare full blast occasions, voltage goes to 11-volts. Any thoughts?

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It's most likely not going to be the fan or the heat sink, so long as they run at all the computer will boot, most likely its the Power supply or mother board. Do you have another computer? Try the powersupply out of it and see if the issue goes away. When it fails to boot is anything displayed on the screen even for a second? Does the fan reach full speed before the Compaq splash screen comes up? – MaskedPlant May 10 '12 at 17:11
1) Eventually I will try another PSU but I was heartened by the fact that 11-v was seen when the fan went full blast. – charlieD May 10 '12 at 17:28
2) Averything is dead when it fails to boot. 3) Very occasionally when the fan comes on full blast for more than 5-sec, the splash screen appears but when the fan slows or stops, the display disappears. – charlieD May 10 '12 at 17:32
Your support page, try the "solve a problem"… – Moab May 10 '12 at 19:37

You should have your power supply tested. You could purchase a power supply tester, or if you like, I'll edit my answer to provide you with detailed instructions as to how to test your power supply yourself with just a multi-meter, but since you are seeing power issues, and you state you have already noticed voltages where they should not be, you should be testing and suspecting your power supply.

Note, I did not just say to go out and replace it. Granted, if you have another power supply, then you could use THAT to test your computer... but I am not saying just run out and buy one. I am saying that yours should be tested.

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