Installing Ubuntu dual-boot

Question

I have used Windows 7 for a long time before and wanted to explore Linux, so I downloaded Ubuntu and made an Ubuntu bootable USB. When I tried to install it in my PC (I have never installed an OS before), I was expecting an option to dual boot (like I saw in some YouTube tutorials) to keep my Windows 7 as it is and try Ubuntu for a few days, but there was no such option.

I tried to run Windows 7 again, but now Windows 7 won't run and I am getting the following error.

Windows Boot Manager  

Windows failed to start. A recent hardware or software change might be the cause.  
To fix the problem:

  1. Insert your Windows installation disc and restart your computer. 
  2. Choose your language settings, and then click "Next."
  3. Click "repair your computer."

If you don't have this disc, contact your system administrator or computer
manufacturer for assistance. 

  Status: 0xc000000f

  Info: The boot selection failed because a required device is inaccessible.

Before installing Ubuntu I had formatted my D drive to install in it, but when I choose the Something Else option during my Ubuntu install, it was displayed as sda3 and I was unable to select it for installation. Now I am stuck without any OS on my computer. Edit:

Do you know, if the Windowsinstallation and the still exists? If you don't know: Boot into Ubuntu as a Livesystem(no Installation) and then you take a look into the "Other Locations" of the file manager and take a deep look into the volumes. There should be an partition with a Windowsfolder in it. (probably on sda2)... — MelcomX, Dec 01 '19 at 09:12
I can't seem to find it. Since I am gettint 'Windows Boot error', does it mean that my windows is corrupted? — AshKB, Dec 01 '19 at 09:22
There are only two options about the reason: 1. Something went wrong but Windows(or the files) is still there. 2. Windows(and the files) isn't there anymore. --> That would meen that the partition was wiped... Could you please post the output of sudo lsblk, that we see, which partitions are still on the harddisk? (boot into live-ubuntu, open a terminal(just press CTRL+ALT+T and enter the command.) Is there any important Data on the Harddisk? (Please forgive me for all English errors) ( — MelcomX, Dec 01 '19 at 12:27
You wiped your Windows, because D was not a disk, but a partition. You don't have Windows any more. All your files are gone. You were warned about it. You can try to get some of them if you stop using the computer and use testdisk. — Pilot6, Dec 01 '19 at 12:47
Fortunately, I had taken a backup of the files before messing with the boot manager. But is there a way to install Windows and Ubuntu simultaneously now? — AshKB, Dec 01 '19 at 12:48
Also, now when I insert Windows disk to install windows, I keep on getting the error 0xc00000f and it doesn't seem to recognise the OS disk. — AshKB, Dec 01 '19 at 12:50
Now you need to install Windows from scratch, then install Ubuntu being more careful. — Pilot6, Dec 01 '19 at 12:50
Possible duplicate of How do I install Ubuntu alongside a pre-installed Windows with UEFI? — Elder Geek, Dec 01 '19 at 21:56
Welcome to AskUbuntu! You may be able to recover your data manually. You may also be able to repair the boot. Please [edit] your question to include a link to a bootinfo summary. Thank you for helping us help you! — Elder Geek, Dec 01 '19 at 22:03
Thanks @ElderGeek ! I actually ended up selecting the first option during Ubuntu installation i.e. to format the computer and install. Since I had backed up only the most important files, now I might to try to backup the secondary ones too using your answer. Thanks for all the help! — AshKB, Dec 02 '19 at 00:13
Possible duplicate of "Install alongside" option missing. How do I install Ubuntu beside Windows using "Something Else"? — Eliah Kagan, Dec 02 '19 at 18:15

Installing Ubuntu dual-boot

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