windows 7 displayed twice on boot up

I recently successfully installed windows 7 on a second hard drive via a usb port on my computer. I no longer have it plugged into the usb port, however, when I boot up the computer, it shows windows 7 twice, and I have to arrow down to the second one, in order to boot the computer up. How can I eliminate the uecessary windows 7 that was related to the usb?