Hi Mr.Shivam -
I'm Kevin B. Independent advisor and Windows 10 user like you. If you purchased your laptop from Dell it should have Windows 10 recovery disk. If you encounter this kind of situation you can use this disk to recover the Operating System or to reinstall Windows.
Insert the disk then turn on your laptop, once you see the spinning circle after the manufacturers logo continually press the F2 or F12 button on your keyboard to get to Recovery environment of Windows.
On the recovery Windows go to Troubleshoot - Advanced Options - Reset this PC
Choose to keep your files and apps, just your files or to keep nothing
Then start the Reset
If the above method don't work it is best to reinstall Windows using the disk that you have.
Thanks.
Kevin b.
Independent advisor.