Xubuntu install fails to boot on its own.
 

Just installed Xubuntu from a USB stick onto my Lenovo Edge Laptop. Single OS setup, only running Xubuntu.

Booting without the USB stick gives me a screen with one blinking _ in the top left corner. Booting the USB stick works fine.
Tried update-grub without the USB stick in the system and rebooted. Still just blinking _.

Any tips would be greatly appreciated.

Tell us how you made this usb. Did you test the download? Did you use the live environment to install it?