I downloaded Ubuntu ISO on my Windows computer and I made a bootable USB. When installing Ubuntu it asked if I wanted to replace windows 8 with Ubuntu and I said yes. This formated my hard drive, but Ubuntu wasn't installed there, it was installed on the USB(not he hard drive), now I have no OS in my hard drive and it only runs when the USB is connected. May I install Ubuntu on my hard drive without using other USB or disk(since I can't).
You will have to recreate the USB drive I am afraid. When you reinstall, make sure you select the computers hard drive as the install destination.