Re: USB Install with no operating system
There are simple ways to repair an infected Win7 PC which involve downloading and burning CDs of free versions of well-known Windows antivirus products. However, if you want to simply throw away your Win7 stuff, files and all, that's your choice.
Ubuntu installation media (CD/DVD/USB) are designed to be used such that, when you boot from them, they give you the option of using the entire drive -- which means you do NOT need an existing OS on the PC to install Ubuntu. You simply boot from the Ubuntu media and select the option to use the entire drive.
Ubuntu 15.04 Mate, Mint 17.1; MS Win 8.1, Win10 TP.
Will not respond to PM requests for support -- use the forums.