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I have a laptop running Windows XP SP3 with one internal hard drive partitioned into C: (system), D: (storage) and I have an external hard drive, F: (external drive). Yesterday the machine was running fine. Today, I go back to it and see that it's just showing a blinking cursor. Checked through the BIOS and the hard drive checked out fine. CTRL-ALT-DELETED the machine a few times, but I was never able to boot back into the operating system. I threw in a live CD and found out that the boot order of the drives has changed. The external drive is now C:, the system partiton is D:, and the storage partition is E:.

Does anyone have any idea of how or why this would have occured? Auto system updates are turned off so there should have been no automatic reboot of the system overnight, and anti-virius runs on the machine and has found no infections before this occured.

Edit When I was looking through the BIOS of the machine, I did see that the boot order was changed. But still the same question remains, what would have caused this to happen? I can't believe that a random reboot happened and totally changed my hard drive setup.

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Did you check the order in BIOS? In most BIOS' you can reorder the harddrives, maybe the BIOS fell back onto it's default settings.

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Yes, I did look at BIOS order and did see that the external drive was now the boot drive. Still I have no idea why that would have occured. would not the internal IDE pick up the internal hard drives before a USB powered drive? – Chris Jan 4 '10 at 21:06
Regardless of how it happened, if the boot order has changed in the BIOS you just need to change it back to how you want it and then everything should boot up nicely. – Connor W Jan 4 '10 at 22:16
@Connor W - The question wasn't asking for a solution since I've already solved that. The question was asked so that I can find what triggers may have caused this problem to arise and so that I can avoid having this happen again. – Chris Jan 7 '10 at 15:59

From experience, some BIOSes on (especially slightly-older but not-too-old) machines will reset (read: mess up) the boot order if they detect new storage devices. I've been victim of this a few times in the past, all you need to do is reboot with an external drive or USB stick plugged in.

The BIOS will detect a "change" of hardware (because it wasn't written intelligently-enough to identify this as a transiently-available device) and as such, either

a) reset the boot order of your hard drives then and there, or as is more likely,

b) reset the boot order of your hard drives the next time you restart without that USB stick plugged in (because it thinks you've removed a disk that had a place in the boot order, panics, and does the wrong thing. At least it had its heart in the right place, bless its poor soul).

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