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PC turns on but won't boot


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#1
xp_even

xp_even

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Since last week, my PC has started acting funny. When I press the power button on my PC, I can hear the CPU fan starting but my monitor displays "No signal". Then I have to switch off the PC and again hold the power button for a couple of seconds. Then it boots up fine.

But about two days back, even this method did not work, so I opened up my cabinet and removed the RAM modules (2x512) and reinserted them. Then, it booted fine again. Till last night, I had to do the same with the RAM to make it boot. The green light on the motherboard glows and even the hard disk appears to be spinning but the lights on the front panel do not glow.

Finally, today morning, even this wouldn't work. I even tried replacing the CMOS battery as suggested in a previous post for a similar problem.

I have a lot of work that I need to do on this PC so please suggest a fix for it.
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#2
phillpower2

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You need to provide more information about the computer!
This should include if it is a laptop or desktop, custom
built or a branded name such as Dell or HP etc, the more
information you provide the better, do you know what MB
is in the computer.
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#3
xp_even

xp_even

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You need to provide more information about the computer!
This should include if it is a laptop or desktop, custom
built or a branded name such as Dell or HP etc, the more
information you provide the better, do you know what MB
is in the computer.


Its an old (three year old) assembled (custom-built) desktop PC with a P4 3.0 GHz CPU, Intel 946GZIS motherboard, Transcend 1GB (2x512) DDR2 RAM @ 667 MHz, Seagate 160GB HDD, 500W PSU, Viewsonic 17" CRT monitor, Samsung 20x DVD writer, XFX GeForce 8600GT 512MB graphics card.
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#4
phillpower2

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My first thoughts are the psu going bad, 500W sounds ok but it is dependent on the quality, performance capabilities & its age, what brand name & model psu is it.

Read Digerati`s canned text on testing a psu;

To properly and conclusively test a power supply unit (PSU), it must be tested under various realistic "loads" then analyzed for excessive ripple and other anomalies. This is done by a qualified technician using an oscilloscope or power analyzer - sophisticated (and expensive) electronic test equipment requiring special training to operate, and a basic knowledge of electronics theory to understand the results. Therefore, conclusively testing a power supply is done in properly equipped electronic repair facilities.

Fortunately, there are other options that are almost as good. I keep a FrozenCPU Ultimate PSU Tester in my tool bag when I am "in the field" and don't have a good spare power supply to swap in. While not a certain test, they are better than nothing. The advantage of this model is that it has an LCD readout of the voltage. With an actual voltage readout, you have a better chance of detecting a "failing" PSU, or one barely within specified ATX Form Factor Standard tolerances. Lesser models use LEDs to indicate the voltage is just within some "range". These are less informative, considerably cheaper, but still useful for detecting PSUs that have already "failed". Newegg has several testers to choose from. All these testers contain a "dummy load" to fool the PSU into thinking it is connected to a motherboard, and therefore allows the PSU to power on, if able, without being attached to a motherboard - great for testing fans, but again, it is not a true load or suitable for conclusive testing.

Swapping in a known good supply is a tried and trued method of troubleshooting, used for years even by pros. If you have access to a suitably sized, spare power supply, carefully remove the suspect supply and replace it with a known good one and see if the problem goes away.

I do not recommend using a multimeter to test power supplies. To do it properly, that is, under a realistic load, the voltages on all the pins must be measured while the PSU is attached to the motherboard and the computer powered on. This requires poking (with some considerable force) two hard and sharp, highly conductive meter probes into the main power connector, deep in the heart of the computer. One tiny slip can destroy the motherboard, and everything plugged into it. It is not worth the risk considering most multimeters, like plug-in testers, do not measure, or reveal any unwanted and potentially disruptive AC components to the DC voltages.

Note the required voltage tolerance ranges:

And remember, anything that plugs into the wall can kill. Do not open the power supply's case unless you are a qualified electronics technician. There are NO user serviceable parts inside a power supply.

Testing the psu should be a priority, because if it goes bang while you are checking things out it could wipe your whole system out, can you loan a psu for testing the other components!

Thanks to Digerati for the psu testing advice.
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