So I am trying to fresh install Windows 10 on my old HP Pavillion 15 laptop however to do this I need to disable secure boot so I can boot from the usb. However my LCD screen is broken on the left hand side so I am unable to see the code I need to type in to confirm the changes. I have tried connecting it to an external monitor but that does not work in the bios. Does anyone know anyway I can do this?
Sorry, but I don't have very good news for you ...
Any external screen you connect is not going to show a display until Windows is loaded, including the video drivers needed to display the external screen. That prevents it from being used to perform any BIOS-related functions.
Sorry, but you would have to get the broken screen replaced -- and that is likely to be quite expensive.