Ubuntu – Gave up waiting for root file system device, in Ubuntu 18.04

I have installed Ubuntu 18.04 on my Dell XPS 15 laptop. I was working fine until yesterday. After a system update, I cannot log in to Ubuntu using normal mode. This is the error I am getting:

Gave up waiting for root file system device. Common problems:

-Boot args (cat /proc/cmdline)
– Check rootdelay=(did the system wait long enough?)
-Missing modules (cat /proc/modules; ls /dev)
ALERT! UUID=22f93100-9860-44b7-8086-51b4404d499d does not exist. Dropping to a shell

BusyBox v1.27 2 (Ubuntu 1:1.27.2-2ubuntu3) built in shell (ash)
Enter 'help' for a list of built-in commands.

(initramfs)

Ubuntu is opening in recovery mode. But there I cannot change the display brightness. In fact,when I did this to check the driver:
ls /system/class/backlight

I found none.

Is there any way I can recover Ubuntu without reinstalling? I have many software's installed and I don't want to loose them now.

Thank you,
Arka