I just installed Ubuntu 14.04 via a USB drive over my Windows 7, and I cannot boot into it without installing the USB. Even with USB installed, it wants me to reinstall Ubuntu every time, even though when I do that it says Ubuntu is installed and asks if I would like to install over it.
I put everything on to the USB with a program in Windows (I believe it was called Universal USB Installer). when I try to boot without a USB, it brings me to a list of boot options, but no matter which I choose, the screen says the following:
Intel UNDI, PXE-2.1 (build 883)
Copyright (C) 1997-2000 Intel Corporation
This Product is covered by one or more of the following patents:
US5,307,459, US5,434,072, US5,732,094, US6,570,884, US6,115,776 and
US6,327,625
Realtek PCIe GBE Family Controller Series v2.35 (06/14/10)
PXE-E61: Media test failure, check cable
PXE-M0F: Exiting PXE ROM