Macbook will not boot from USB

Thanks for the link but it doesn't work. When I try to boot from the USB stick it just gives me a white screen and a curser.

Its an intel so apparently I am supposed to hold down the option key when booting but nothing happens.

I know the computer works ok as I can put the hard drive back in and off it goes and the usb sockets are working.

I just want to reinstall Lion OS to an SSD.

Thanks

idk why but I put High Sierra on the USB boot and now its installed and working fine.