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I bought a new graphic-card and put a spare hard-drive in my old pc (got myself a new one). Then I installed freshly Windows 7 professional again and the PC worked fine for a few months.

I don't know if this is relevant, but if the PC wasn't used for a while it went into sleep mode, sometimes left alone for a few days, but mostly used a few times a day.

Then sometimes the PC gave a blue screen, when it did, I just rebooted the PC to find it running fine again for some days. This went on for quite some time until one day it became so bad that I decided to try to repair the thing later on and put it away for now.
The symptoms the PC was showing near the end was the following:

  • Regular blue screens, sometimes minutes in between.
  • Hangs right after logging in.
  • In the end the PC would just go on, and do nothing pretending it was very busy with something.

This is what I tried to find/solve the problem:

  • I checked the hard-drive for errors and bad sectors, only minor stuff got fixed when running a check disk
  • Checked CPU temperatures right after the crash and regular when running, it would never go above 50 degrees Celsius.
  • GPU temperatures even lower temperature than the CPU
  • Re-seating ram didn't work (there are two chips of 1GB each)
  • Removed the battery to clear the CMOS
  • Booting without:
    • The back-fan connected
    • CD- drive
    • Front usb panel
    • Hard drive
    • Graphic card (an other one than I gave her because that one was transferred to her 'new' pc)

I postponed the research for a bit more than 2 months. And today I tried it again. Unto my surprise the computed seemed to boot (I got to see the BIOS!!!). So I quickly entered the bios, checked the settings and monitored the temperature of the CPU.
Everything looked fine so I continued booting, I got the login screen of W7, entered the password and the computer froze on 'Welcome'.

I'm pretty much out of options and I suspect the motherboard, but I do not understand why it would work after being down for a few months.

The current computer state: I put the computer on and the 'busy' led indicates it does something, that is it. Nothing on the screen, no beeps about missing crucial hardware. I do hear the disk spinning up though, but I guess that is only because it gets power. I left it on for an hour to see if it just had gotten really slow, but it was still doing the same thing.

My question: What can be the cause of this weird behaviour and how to fix it?

Please leave a comment if something is unclear or more information is needed.

Solution: One of the ram chips wasn't 100% functioning. A classic hardware fault. However, I still would like to know, why it would work sometimes.

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2 Answers 2

up vote 1 down vote accepted

This kind of behaviour usually stems from one of three causes: 1) a thermal problem, 2) a power problem, or 3) a hardware fault.

It seems like you excluded 1). Now you need to exclude 2). Check how much rated power your PSU is providing and if it is at least 25% higher then the combined power requirements of your components, esp. GPU and CPU. Even if the PSU has a high enough rating, try another PSU with sufficent power output.

After that you are down to faulty RAM or a broken motherboard.

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I will try another PSU, though the current one should be sufficient. But it still doesn't explain why it worked again after being off for 2 months. –  Mixxiphoid May 2 at 17:05
    
I tried another PSU, but the problem persisted. However, a few hours after asking this question (and before trying a different PSU) the computer worked again, I was able to install ubuntu, but after I shut it down, I could not make it boot again :(. –  Mixxiphoid May 3 at 14:20
    
You have a hardware issue, you need to isolate the faulty part of your equipment. I take you have a second machine available? The course should be clear. –  bjanssen May 3 at 19:42
    
Plenty machines available here :). I just removed one of the ram chips, it seems to boot again. If it stays like this for 24 hours, it is probably the ram chip. But then I still don't understand why it would function sometimes. –  Mixxiphoid May 3 at 20:15
    
Turned out one of the ram chips was defective. However, it was not always defective, very weird. Beside that, sometimes the hard drive has spin-up problems. –  Mixxiphoid May 6 at 19:15

I think it can be because of your RAM. May be the RAM is going to die.Check by removing one RAM at a time. As you told that the Busy led of HDD is glowing it can also be a cause with the HDD Cable, usually seen with SATA Cables...

Check it and report.

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You clearly did not read the whole question as I already stated that one ram chip is faulted. The question remains however why it would work sometimes even though it is broken. –  Mixxiphoid May 10 at 6:27
    
Yes. I understand that. Broken RAM chips behave unexpectedly. That is, sometime it works well,sometimes not. Try removing the broken RAM and run your pc only with one RAM. –  FaheemMCFC May 10 at 9:04
    
Again you either did not read the question or did not understood it. You are only telling me that which I already have found, I'm asking for an explanation of the WHY. The problem itself is already solved. –  Mixxiphoid May 10 at 9:32

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