I dual booted Ubuntu 18.04 on Windows 8.1 OS. It worked fine for 2 days. Then I started it today and it was taking long time to show the screen which asks user to choose the OS. The screen was stuck at the screen which shows options for Booting etc. So I switched off the PC directly by long pressing the power button on CPU. And then I started my PC again, but this time there was no display on the monitor and even Num-Lock key was on despite pressing the Num-Lock button. I guess the system got hanged. I am worried about my data. What could be the possible reason for it and please suggest some remedy. I didn't even take any backup of my files while installing Ubuntu.