It worked for:
Ubuntu 18.04.6 LTS
Alienware-17-R5
Intel® Core™ i7-8750H CPU @ 2.20GHz × 12
NVIDIA GeForce GTX 1070/PCIe/SSE2
GNOME 3.28.2
OS type 64-bit
1. Get to the Grub page (turn on computer and press Escape (in UEFI) or Shift (in BIOS) after you see the computer logo)
2. Select “Advanced options for Ubuntu“
3. Enter the Recovery Menu (select Ubuntu, with Linux-*** (recovery mode))
4. You might need to select “network” to make sure you are connected to the internet
5. Select “root”
6. sudo apt-get install xserver-xorg-input-all