I installed ubuntu in my lenovo notebook already running Windows 10. Followed the instructions given in the website https://www.tecmint.com/install-ubuntu-16-04-alongside-with-windows-10-or-8-in-dual-boot/comment-page-14/#comments. After installing I am unable to boot into both Windows 10 and Ubuntu. I don't get the boot options screen. Only the error message "Unable to boot Ubuntu". I tried boot-repair tool and obtained the following diagnosis report http://paste.ubuntu.com/p/wrZyxsG9zW/. I am able to run live-ubuntu from installation disc. Appreciate any help.
Windows is BIOS/MBR and it looks like you forced an UEFI install of Ubuntu on a MBR(msdos) partitioned drive. Normally UEFI uses gpt partitioning. But Windows in BIOS boot mode must be MBR and boot flag must then be on the NTFS partition with Windows boot files or your sda1.
You show errors on NTFS sda2, not sure if just Windows 10 hibernation or it needs chkdsk which you can only run from Windows or Windows repair disk or installer with repair console. Use gparted and move boot flag back to sda1, see if Windows boots or if f8 takes you to repair console.
First fix Windows, chkdsk and turn off fast start up, You need to make Windows repair flash drive as you will need both Boot-Repair/Ubuntu live and Windows repair flash drives with BIOS/MBR.
Then use Boot-Repair from Ubuntu live installer booted in BIOS/Legacy/CSM boot mode and in advanced mode do a full reinstall of grub2, so it is the BIOS boot version of grub. You do not need to reinstall Ubuntu, just grub2.
Windows 10 works better dual booting in UEFI mode. Windows will, with updates, turn fast start up back on. Then grub will not boot it and you only can then directly boot using Windows boot loader. With UEFI, you can choose that from UEFI boot menu. But with BIOS, you only have one MBR and then have to temporarily restore Windows boot loader, fix Windows & then restore grub to MBR.
Since you have newer UEFI hardware, the other option to to reinstall Windows in UEFI boot mode. But that will erase system, and you need good backups of all your data & configuration. How you boot install media UEFI or BIOS, is then how it installs for both Windows & Ubuntu.