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I have a 750 GB HDD with two partitions. One partition has 550 GB with my files so I want to save it. The other partition had Windows 7 on it.

So I booted Windows 10 from USB, formatted the Windows 7 partition but I was unable to install Windows 10 because it requires GPT partition table. The current table format is MBR.

So now I am unable to install Windows 10, also I am unable to install Windows 7 because in will not boot, giving some disk error.

I booted again from Windows 10, deleted the formatted Windows 7 partition, tried to create it again, but the space remains unallocated.

I don't want to loose my files so I can't reformat the entire hard drive as GPT. DISKPART will only list the entire HDD so I can't work with it.

Any suggestions please, to save my data and install Windows 10?

  • If you already formatted the drive, I don’t understand, Windows 10 also supports MBR. Requires you to enable legacy mode in order to boot into the installation environment in the supported mode. – Ramhound May 5 at 8:37
  • I don't know what to do. I can't copy my files to an external hdd because I don't have an installed os. Legacy mode is enabled but only Windows 10 is able to boot but I can't install it because of partition table error. – J Doe May 5 at 9:01
  • If you enable Legacy Mode/CSM and have booted into the Windows installation environment then you should absolutely be able to select a partition and install Windows. – Ramhound May 5 at 10:20
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First things first: make backups now. If that data has any value to you, you should make regular backups. Hardware sometimes fails, humans make mistakes, malware is doing its malware stuff. You must have backups of anything that you can't loose.

You can install either Windows 7 or Windows 10 on MBR disk, but you have to boot the installation media in CSM mode (aka. BIOS mode aka. legacy). It sounds like you're booting in EFI mode, which makes Windows require GPT.

So:

  1. Make backups, don't take risks.
  2. Boot in CSM mode instead of EFI mode.
  3. Install Windows as usual.
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  • I don't know how to backup my files without having an installed os on my computer. My bios only let's me to enable/Disable legacy mode, I have no other options regarding boot method. Legacy mode was always enabled. If I disable it, the Windows 10 flash drive is not listed in boot device list. – J Doe May 5 at 8:59
  • How did you get the Windows 10 flash drive? Did you create it yourself? – gronostaj May 5 at 9:18
  • It is an original windows 10, probably, it is not mine. I did not created the usb drive myself. Is it possible to have it burned in a wrong way on the USB flash drive? I just received it with the serial number written on a piece of paper. – J Doe May 5 at 9:24
  • @JDoe - Yes; You will need to create the installation media yourself and make sure its created to support legacy mode. – Ramhound May 5 at 10:20
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    Thanks for your suggestions guys. Sorry for my lack of knowledge, I will try ți backup with Ubuntu first( 500gb of data will take forever on USB 2.0). Then I will create a bootable flash drive with new Windows. I will give you feedback about the results. Thanks. – J Doe May 5 at 10:40
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Problem solved, thanks guys. I used Rufus to write the windows for MBR/BIOS to the USB flash drive. After booting, I was able to create a partition from the unallocated space and windows is now installed. Saved my files and windows is running fine. Thanks again.

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  • That should have been a comment, sorry. – J Doe May 5 at 18:29

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