I tried to start my Mac & a folder with a question mark appeared.
I researched on Google and discovered it was a problem with the Boot partition. I saw how to fix it. I used Opt ⌥ while booting and I was able to get to Mac Internet Recovery.
I tried to install new software, after agreeing to terms and conditions, it took me to the next screen where I had to choose the Install destination. But it was blank - There was no Macintosh HD hard disk icon present there.
When I went to Disk Utility, There was no Macintosh HD there either. When I researched on SE, one similar questions was asked - the solution said that there would be a drive named super disk. But here in my Mac there is no super disk. Only a single disk 2 GB drive.
I understand the disk may be dead but it could be also because of a loose connection as I recently opened my Mac.
Update (5 Months after asking question): When the Genius Bar took a look at it, they found out that the disk had died. I got it replaced and now it works perfectly.