If you plug the Live USB into the PC and turn it on and you keep getting an error message about "no operating system found" or your usual operating system keeps loading then you need to find out what button you can press while the PC starts to get a boot options menu and choose the USB.
It's usually F9
in HP laptops, and similar buttons in other PCs.
This page has some laptops and motherboards and their respective boot options keys https://kb.wisc.edu/page?id=58779
If you can't find your PC model or it didn't work, try to google your "<PC model here> boot options menu"
and you should get a button you can press as soon as the PC turns on and it should show a boot menu.
If all else fails, try pressing the ESC
key and enter the BIOS. Go to boot options and change the boot order to have the usb at the top of the list. Save and exit.
If you press "Try Ubuntu" in the Live USB and get a black screen, then it's probably a graphics issue.
If the "Try Ubuntu" option is in a menu in the middle with 4-5 other options (meaning it has booted in legacy or csm legacy), press F6
on the keyboard, choose nomodeset and press Enter
, then press Esc
to go back to the menu and press on "Try Ubuntu".
such as the picture below
If the "Try Ubuntu" option is in a black and white menu at the top (UEFI) such as the picture below, then you'll have to manually add the option for the graphics.
Highlight the "Try Ubuntu" option and press E
on your keyboard.
Go down to the line that says "linux /boot/vmlinuz ...... quiet splash"
and edit it so that it has "nomodeset" at the end instead of quiet splash
e.g. "linux /boot/vmlinuz ..... nomodeset"
Then press F10
on your keyboard to boot as seen below.