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Yesterday I was just browsing Stack Exchange when my computer suddenly froze. I've been having what I assume to be power supply issues the last couple weeks, so I've been used to it crashing and freezing a couple times a day, but when I tried to reboot this time, it said that the NVIDIA Boot Agent failed to detect my primary boot disk.

I thought that my hard drive crashed, but I started up an Ubuntu live CD(interestingly, the installer said that it failed to open), and now I can access the files on my hard drive fine now and it passed a SMART test. What could cause something like this?

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Why the close vote? –  Shinrai Jan 24 '12 at 15:29
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Generally a power supply issue is characterized not by freezes and crashes but by the computer power down completely, especially at times of high load, such as playing games or watching video (the Video Card generally being a super-high-drain device).

Freezing and crashing sounds to be more likely a hard drive issue, taken together with your other symptoms.

I would get a replacement drive and install the OS to that, keep this drive as a secondary or backup just until it completely fails, never leaving anything just on it (always copied elsewhere too).

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No, I've seen it crash three different ways(the screen just turning black; the everything just freezing, possibly with some tearing; and with a BSOD). It doesn't seem related to power usage, but if my hard drive crashed, wouldn't it stop working? I can still use it fine from this Ubuntu Live CD. –  Ullallulloo Jan 24 '12 at 15:00
    
It depends on if the drive stops spinning or merely has bad sectors that happen to fall where some driver is expecting to find something it needs, which sounds more plausible. Run a scan disk or repair from the Windows installer disk and see what it finds. –  music2myear Jan 24 '12 at 15:03
    
I ran a SMART test, and it said it didn't detect any bad sectors. –  Ullallulloo Jan 24 '12 at 15:52
    
Then you'll need to diagnose the rest of the hardware, piece by piece, as in normal hardware diagnosis. –  music2myear Jan 24 '12 at 15:57
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Actually that's the worst way to test hardware. (don't stick in other machine) Any "GOOD" IT shop will be able to troubleshoot the powersupply... (there are testers... but I doubt a home-user would want to invest in one)... as well as software tools for testing video cards/processors (OCCT is my favorite) etc... In short... if you aren't used to this sort of thing... might want to find someone who is. –  TheCompWiz Jan 24 '12 at 16:29
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If indeed your power supply is failing, it's very likely that your hard drive isn't getting sufficient power to spin-up. Booting from a CD takes significantly less power and may give the HDD sufficient time to spin-up before being accessed.

That being said, most of the time the problem is not the power supply—it could be, but that's just my own experience. There may be other issues at play here. I would start with the usual diagnostics to figure out what is bad. (check RAM, run some sort of disk tools, etc...)

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I've checked my RAM, and my power supply works fine most of the time, just it dips a few times a day. Also, I can spin up my hard drive still, as I'm copying some files off of it right now. –  Ullallulloo Jan 24 '12 at 14:50
    
What is your evidence that optical drives use less power on boot than HDDs? You may be correct, I'm just a little skeptical. –  music2myear Jan 24 '12 at 14:51
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@music2myear look at the power-requirements for optical drives... and those of hard-drives (platter-based). For the more practical analysis... optical drives spin nowhere near as fast as platter-based drives. –  TheCompWiz Jan 24 '12 at 14:53
    
Even if an optical disk uses less power in a boot environment, your computer is still spinning up the HDDs too at the same time, if the HDD is in the system. If you are booting from a CD and have an HDD in the computer, you're spinning up the HDD AND the optical, not just the optical. If you're spinning up only the HDD, the optical may spin up briefly, but then it stops and doesn't run again until called upon. –  music2myear Jan 24 '12 at 14:56
    
@music2myear as he is using an "Nvidia Boot-Agent" more than likely the disk-controller supports hot-swapping... and as linux is smart enough to handle hot-swapping... the initial boot does a "reset" on the disks during the driver initialization. i.e. problem detecting drive at BIOS... but when OS boots... driver resets... and re-detects the drives. –  TheCompWiz Jan 24 '12 at 14:59
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It sounds like it's just damaged your bootloader. If it crashed at the wrong time, while it was doing something to the bootloder, that's quite possible. To fix it, boot from your Windows install disc and tell it to Repair.

If you're using Fedora, boot to a live CD and run /sbin/grub-install BOOTDEVICE

  • where BOOTDEVICE is usually /dev/sda (If you get an error '/dev/sda does not have any corresponding BIOS drive' from that, then try /sbin/grub-install --recheck /dev/sda). For Fedora 16 and later, use /sbin/grub2-install instead of /sbin/grub-install.

I'm afraid I don't know what to do if you're using Ubuntu. Might be the same as with Fedora.

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My main OS is Windows 7, I'm just using Ubuntu to back stuff up and do tests. I'll try these. –  Ullallulloo Jan 24 '12 at 17:06
    
Alright, I figured that's how it was; just wanted to cover my bases. –  SaintWacko Jan 24 '12 at 17:40
    
Okay, I tried Windows 7's repair tool, but it said it couldn't detect my hard drive either. –  Ullallulloo Jan 24 '12 at 17:44
    
Do you have another computer you can try putting the hard drive in? That would tell you if there's a hardware issue. –  SaintWacko Jan 24 '12 at 19:17
    
Yeah. I can access it from this Ubuntu Live CD, but I'll probably try that too. –  Ullallulloo Jan 24 '12 at 19:18
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