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Pc not booting. Screen remains black. What next?

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Hi guys

I am really desperate. I should work on my thesis. Why does my PC break down now?

Short description:
PC does not start. Screen remains black. Fans run. No beeps (but not sure if my PC speaker is actually connected).

Longer, more detailed description:
I never shut down my PC. I always put it in Standby. Works perfectly.
3 days ago, when trying to awake it from standby:
- The fans start
- the LEDs (HDD, power) go on
- Screen remains black (monitor not turning on, actually. So no signal.)
- waiting (sometimes it needs longer to get out of standby)
- pressing reset: nothing happens.
- turning power off, turning power on
- Fans still starting
- IMPORTANT DETAIL HERE: When I start my PC and it was NOT in standby, the fans sound different. One of the Fans runs at full speed, being really loud. After a few seconds, it slows down, then it enters the bios, starts normally. If I awake my PC from standby, this does NOT happen. The fans run quietly from the beginning.
So in this case, after unnplugging and replugging, I expected the other start sequence with the fans being loud. Did not happen. Still slow.
- screen remains black
- I retry two or three times, I am desperate.
- I get my stuff, screwdriver and everything, prepared to open my PC and check for loose wires, whatever....
- I think: Lets give it one more try before I open it: I replug the power cable and start it
- et voila: It works!
- PC ran fine for three days. Was several times in standby, always awoke, always working.
- I play games, I work with the mashine, I watch DVDs and BluRays. I play hardware demanding games. But my system does not run hot. Lots of fans installed...

Today, this morning:
- Same problem, screen remains black. LEDs on. Fans run slowly. System does not wake up. Screen remeins black (monitor not turning on, actually)
- Unplugging, waiting, replugging, turning on.... nothing.
- I open the case. I unplug all HDDs
- replug power, same problem.
- I unplug the power, take out first one, than the other RAM (running dual channel)
-> no effect
- checked all plugs

Now what should be my next step?
What can be faulty? I think I excluded the RAM. And since the problem actually happened before but the problem sort of vanished and then the PC ran smoothly for 3 days straight under stress, I don't think there is something substantially damaged.
But what can it be?
Bios? Power Supply? Or is the CPU or Graphics adapter faulty?
I do not have a second PC nor do I have a friend with a PC near me. So I can't exchange components easily.
Can someone help me?
I'm desperate. I don't know what my next step should be. I think I will try to reset the bios. Could it be bios related?

CPU: Intel Core2Duo
Mainboard: P35C-DS3R
Graphics Adapter: Nvidia geforce 260 something... <-All cables connected. Including the additional 2 power cables. Checked that.
RAM: 2*2GB KIT from Kingston? King-something?

Edited by Finsch, 03 December 2010 - 07:02 AM.

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    Grumpy Ol' MSgt (Ret.)

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The first thing I would want to verify is that there is good power. Following is my canned text on testing PSUs:

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.

Note the required voltage tolerance ranges:

Posted Image
NOTE: Disregard the -5VDC reading. It is no longer used.

Swapping in a known good supply is a tried and true 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 the 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.

The voltages can be checked in the BIOS Setup Menus of most motherboards but they do not reveal ripple or other anomalies either. And the Setup Menu places very little demands on system resource so, like the temperature readings found in BIOS Setup Menus, they may not reflect values obtained when the computer is processing demanding tasks.

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.

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I do not have a spare power supply, nor do I have a spare system I can check this power supply with.
But I ran some other tests:
I plugged in another Graphics Adapter -> no changes
I testes if the PC speaker is connected, it is -> no beeps
---> my system does not even beep! If it would at least beep I would have some hopes....

Why does this have to happen now....
I will try to bring this PSU to a dealer and see if he can check if it works.
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    Grumpy Ol' MSgt (Ret.)

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I will try to bring this PSU to a dealer and see if he can check if it works.

Sounds like a plan.
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