Laura..
I work on computers for a living there hasn't been one computer I have not been able to fix with the directions I posted above.
When you are using a USB you need to find out what your computer's brand F-key is to load the boot menu. Once the menu comes up select the USB drive from the list. It will come to a menu that wants to know where you want to install it to. Blow out the old partition and reformat it and install it there..
Rick