I am new to linux(ubuntu) and have installed it while following different blog posts and stuff to keep my Windows installed and I hope it is. I selected Something else option while installing but now when I boot it does not display any option to boot with my Windows. I have DELL laptop, it had Windows 8.1 installed.
This is the boot repair report. And yes, this is not duplicate of this.
I'm afraid you've accidentally deleted Windows from your computer. In your Boot Repair output, lines 57-61 show your partitions, which include an EFI System Partition (ESP) to hold your boot loaders (/dev/sda3), a 14GiB root (/) partition (/dev/sda1), a /home partition (/dev/sda4), and a swap partition (/dev/sda2). There are no Windows partitions among that list. Your ESP does include the Windows boot loader, but that's pretty much all that remains of Windows on your computer, aside from ghosts of former files. (See below for recovery tips.)
There is considerable free space on the disk -- your final partition ends at sector 95,688,703, but the disk has 976,773,168 sectors. Thus, there's a slim chance that you'll be able to recover your Windows partition(s) with TestDisk or a similar tool. I say "slim chance" because the usual way to install Ubuntu alongside Windows is to shrink the largest Windows partition from its end point, which puts Windows near the start of the disk and Ubuntu at the end or in the middle of the disk. That's not the pattern here, but if you moved and resized your Windows partition so that it started somewhere after sector 95,688,703, you might be able to recover it. It's worth a try.
If that fails, I hope you have good backups, since restoring your user files from backups is your best bet. If not, you'll need to use PhotoRec or something similar to recover your files one-by-one. (I've seen claims that third-party Windows-specific tools do a better job than PhotoRec on NTFS volumes, but I don't have pointers to specific tools. You might want to ask about this on a Windows forum.) Also, if you had important files on your system, stop using it immediately!! Every moment that Ubuntu is booted from that disk, it may be writing data to disk, possibly overwriting your old Windows data. Shut down and use an emergency disk for recovery.
If you don't care about personal files from your Windows installation, or after you recover then with PhotoRec or something similar, you can re-install Windows to the disk using emergency media. This page provides instructions on downloading various versions of Windows legally for situations like this.
Before you re-install Windows, though, consider resizing your Ubuntu partition; 14GiB is a bit small for Ubuntu. It's adequate if you don't install much extra software, but it may well run out. Unfortunately, since that partition is at the start of the disk, you'll need to move or resize others. The easiest way may be to delete your swap partition (/dev/sda2), expand /dev/sda1 into that space, and create a new swap partition later on the disk. This will require editing /etc/fstab to point to the new swap partition once you're done; failure to do so will mean that Ubuntu will not use the swap partition at all.
