not able to install the ubuntu os

[Shrey Saini]

i am not able to install ubuntu 16.04 or 18.04 anyone
its always ending with fatal error grub-install cant be executed

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: ubiquity 2.21.63.7
ProcVersionSignature: Ubuntu 4.15.0-29.31~16.04.1-generic 4.15.18
Uname: Linux 4.15.0-29-generic x86_64
ApportVersion: 2.20.1-0ubuntu2.18
Architecture: amd64
CasperVersion: 1.376.2
Date: Tue Oct 16 00:17:49 2018
InstallCmdLine: BOOT_IMAGE=/casper/vmlinuz file=/cdrom/preseed/ubuntu.seed boot=casper only-ubiquity quiet splash ---
LiveMediaBuild: Ubuntu 16.04.5 LTS "Xenial Xerus" - Release amd64 (20180731)
ProcEnviron:
 LANGUAGE=en_IN
 PATH=(custom, no user)
 LANG=en_IN
 SHELL=/bin/bash
SourcePackage: grub-installer
UpgradeStatus: No upgrade log present (probably fresh install)