missing grub cannot boot into ubuntu

My system dual booted with windows and ubuntu16.04LTS was working fine but one day when i start my system it shows checking disk errors.. i wait and then it boots into windows directly without giving me any option.. i tried to boot from the boot menu by pressing f12 at the starting but there is no ubuntu option now.. i am sure ubuntu is still present in the partition i have checked that.. i have tried many things available online but none of them seems to work in my case ex: i tried easybcd which says boot is efi mode and therefore i cannot add any linux boot to it.. i also made a bootable pendrive to install boot repair but i think its no longer available.. i dont know.. can someone please help me to fix it?.. thanks in advanced.