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Startup error (fatal system error) after downgrading Win10 to Win7

Discussion in 'Windows 7' started by chevrolab, 2016/02/19.

  1. 2016/02/19
    chevrolab

    chevrolab New Member Thread Starter

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    I upgraded Windows 7 to Windows 10, but had decided to downgrade it. The startup error happened after the previous Windows has recovered and my laptop rebooted.

    I didn't do any backup before downgrading. The only software change that I know was the antivirus update from Win7 to Win10 version.

    This screen appeared at startup:

    STOP: c000021a {Fatal System Error}
    The verification of a KnownDLL failed. system process terminated unexpectedly with a status of 0xc0000020 (0x86365420 0x00000000).
    The system has been shut down.

    I tried rebooting, and "Launch System Repair (recommended)" option. But after choosing that option, the startup repair didn't run and the previous error screen appeared.

    I tried launching Advanced Boot (pressing F8 key) and chose "Last Known Good Configuration" option but the error screen reappeared.

    I found a seemingly similar thread in this forum and tried the command prompts given by the staff but the same fatal error screen appeared.

    I haven't tried other suggestions further down in that thread.
     
    chevrolab,
    #1
  2. 2016/02/19
    Evan Omo

    Evan Omo Computer Support Technician Staff

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    Hi chevrolab, Welcome to Windowsbbs! :)

    Can you boot the computer into Safe Mode or does the same blue screen message appear? Have you gone into the advanced recovery options and tried choosing a System Restore point to restore your computer to before this problem occurred?

    If you are stuck and none of those options allow you to get into your Windows 7 system, then you will need to take out the hard drive and hook it up to another computer to get the data backed up. Then once the data is safe you will need to perform a clean install of Windows 7. Do you have a Windows 7 DVD?
     
    Evan Omo,
    #2


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  4. 2016/02/19
    chevrolab

    chevrolab New Member Thread Starter

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    Hi, and thank you for you reply :)

    I could log into safe mode before, but now the loading has been going on for an hour.

    The downmost process is this:
    Loaded: \Windows\system32\DRIVERS\CLASSPNP.SYS

    I learned that to go to advanced recovery options I must be able to access control panel (and I can't).

    I will have my hard drive backed up. And I don't have Windows 7 DVD.
     
    chevrolab,
    #3
  5. 2016/02/19
    MrBill

    MrBill SuperGeek WindowsBBS Team Member

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    MrBill,
    #4
  6. 2016/02/20
    Arie

    Arie Administrator Administrator Staff

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    What hardware is this on? I'm suspecting that your BIOS is set to use UEFI. Windows 7 can't use that, and UEFI sees this as a violation.

    You'll have to disable Secure Boot in your UEFI BIOS, or switch to Legacy BIOS Mode.
     
    Arie,
    #5
  7. 2016/02/20
    chevrolab

    chevrolab New Member Thread Starter

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    I managed to log into safe mode after several tries and did backup.

    I have my product key but unable to get a copy of Windows
    _
    Error
    We encountered a problem with the product key you provided. Please try again or visit the Microsoft Support Contact Us page for assistance.
     
    chevrolab,
    #6
  8. 2016/02/20
    chevrolab

    chevrolab New Member Thread Starter

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    Ah I didn't know this, should've altered it before downgrading my OS.
    Disabling Secure Boot isn't possible because my current BIOS isn't UEFI.
    Is it possible to get into UEFI bios? (Though I think no.)
     
    chevrolab,
    #7
  9. 2016/02/20
    Evan Omo

    Evan Omo Computer Support Technician Staff

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    Press F2 or the Delete key when the computer first boots up to enter your computer's UEFI and look for an option for Legacy Boot mode and enable that option. Then save the changes and see if Windows 7 boots normally.

    If that does not work and you can't get your Windows 7 ISO file from the Microsoft website then use the alternate method below.

    You will need to create a Windows 7 DVD to repair the Windows 7 OS. You can find Windows 7 SP1 ISO files here, Windows 7 SP1 ISO Image Downloads.

    You will need to download a torrent client to download the Windows 7 ISO image. Download the portable version of uTorrent and run the program.

    After the program opens, click on the add link button and paste the download link of the Windows 7 ISO file that matches the version of Windows 7 that you have installed.

    Once you have downloaded the ISO file you want, download and run the portable version of Active ISO Burner and burn the Windows 7 ISO file to a DVD.

    After you have created your Windows 7 DVD follow the instructions from here to perform a clean installation of Windows 7, How to Do a Clean Installation with Windows 7.
     
    Evan Omo,
    #8
  10. 2016/02/29
    chevrolab

    chevrolab New Member Thread Starter

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    There is no Legacy boot option in my BIOS.

    Now I have done clean install of Windows 7 by downloading the ISO file. But instead of using DVD, I used USB device following the instructions here.

    I have yet to activate my Windows (will do). What do I need to do next?

    I have a question, now my display is stretched but I've set it to recommended resolution, how to alter this?
     
    chevrolab,
    #9
  11. 2016/03/07
    Evan Omo

    Evan Omo Computer Support Technician Staff

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    Did you install the drivers for your hardware devices? You will need to install the drivers for your motherboard chipset, video, audio, and network devices if you haven't already done so.

    Are the specs of the machine the same as those listed under your My System area in your profile?
     
    Evan Omo,
    #10

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