Dual boot system directly booting into windows

 I suddenly booted my system into windows after ages and after restarting I was not able to see the grub loader option, so I was not able to select UBUNTU my favorite choice of operating system. It was directly login into windows os

But Thankfully I could resolve it using the following.

1.  Search for advanced start up option.
2. Click on restart now in next menu.
3. In the following menu click on trouble shoot.
4. Click on advance option.
5. Restart the computer.
6. System will now boot into BIOS. 
7. Go to Boot order section using arrow keys
8. Change the order by enter and drag
9. press f10 to accept the changes.
10. then escape.

 

This can also be done by pressing f10 while booting and directly go to BIOS. choose the boot order preference.