Possibly the installation media is corrupt/damaged.
I recommend downloading the .iso again, and then after the download is complete, verify the file using a hash function. You can see the hash files listed alongside the .iso's:
http://releases.ubuntu.com/18.04/
Here's a more complete tutorial on that, if needed:
https://tutorials.ubuntu.com/tutorial/tutorial-how-to-verify-ubuntu#0
Once you have a known good .iso, install it onto a freshly formatted usb flash drive. On your first boot of the flash drive, instead of trying Ubuntu, select to "Verify boot media". This will run an additional check to ensure the .iso was written to the USB drive without error.
If that also completes without error, try installing Ubuntu onto your laptop again with this verified image and known good installer.