Dual Boot (Coexisting with Windows) Won’t Boot: Causes and Solutions

Many users install both Windows and Linux on the same computer. This setup is called Dual Boot. It is convenient, but after a system update, partition changes, or bootloader problems, the system may fail to boot properly.

Sometimes the PC goes straight into Windows. Sometimes it gets stuck at GRUB. In other cases, neither Windows nor Linux will boot. Below are the most common causes and ways to fix them.

1. First, identify the exact symptom

The computer boots directly into Windows
The GRUB menu appears, but Linux will not start
The GRUB menu appears, but Windows will not start
Only grub rescue is shown
You see no bootable device or a similar error
A black screen appears, or the system freezes at the manufacturer logo

2. Most common causes

A Windows update changed the boot order
GRUB is damaged or has been overwritten
The EFI partition has problems
The BIOS/UEFI boot order was changed
Fast Startup caused partition state issues
After resizing or changing partitions, the boot information no longer matches
Windows Boot Manager or Linux boot settings are corrupted

3. First, check the BIOS/UEFI boot order

If the computer always goes directly into Windows, the first thing to check is the boot order. After a major Windows update, Windows Boot Manager often gets moved back to the top of the boot priority list.

Restart the computer
Press F2, Del, Esc, or F12 during startup to enter BIOS/UEFI
Find the Boot settings
Check what the first boot option is

4. If you can only boot into Windows

This does not necessarily mean Linux was deleted. In many cases, GRUB is simply no longer being called first.

Check whether the Linux partition still exists
Check whether a Linux boot entry still exists in BIOS/UEFI
Check whether the boot mode is still set to UEFI

5. Repair GRUB using a Live USB

sudo fdisk -l

Assume the Linux root partition is /dev/sda3 and the EFI partition is /dev/sda1:

sudo mount /dev/sda3 /mnt
sudo mount /dev/sda1 /mnt/boot/efi
sudo grub-install --boot-directory=/mnt/boot /dev/sda
sudo update-grub

If the normal method does not work, you can also repair it using chroot:

sudo mount /dev/sda3 /mnt
sudo mount /dev/sda1 /mnt/boot/efi
sudo mount --bind /dev /mnt/dev
sudo mount --bind /proc /mnt/proc
sudo mount --bind /sys /mnt/sys
sudo chroot /mnt
grub-install /dev/sda
update-grub
exit

6. If Windows will not boot

bootrec /fixmbr
bootrec /fixboot
bootrec /scanos
bootrec /rebuildbcd

After repairing Windows, you may also need to repair GRUB again.

7. Pay attention to Fast Startup and UEFI/Legacy mode

Turn off Fast Startup in Windows first
Ideally, both Windows and Linux should use UEFI
Or both should use Legacy BIOS

If one system uses UEFI and the other uses Legacy mode, boot problems are much more likely to happen.

8. Summary

When a Dual Boot system fails to boot, it usually does not mean the entire system is gone. More often, the issue is related to the boot order, GRUB, the EFI partition, or boot changes caused by a Windows update.

First, check the BIOS/UEFI boot order
Confirm that both Windows and Linux partitions still exist
Use a Live USB to repair GRUB
Repair Windows Boot Manager as needed