Can't Boot Computer (Media Test Failure)

Yesterday while watching an online baseball stream and simultaneously browsing facebook, my computer randomly gave me an error message. Unfortunately I don't remember what the message was about. What I do remember is that I immediately opened a new firefox tab and searched up the error. I clicked on the first link, and the OP was talking about how he had received the error and shortly after, his computer shut down. Almost on cue, my computer crashed and restarted itself.Ever since then, I can't boot up my computer properly.I turn on the computer, I see the first two screens that I always see (BIOS screen and then the 'Detecting eSATA drives' screen). After this it goes to the third screen, which I also always see. But this is where the problem is.First it loads all that code crap that I never understand. Then, like always it gives me these two lines: 'Verifying DMI Pool Data....'And then 'Boot from CD'. This always happens. But regularly from here it just boots up and goes to the Windows loading screen.Now, on the same screen, it starts giving me error messages.

NVIDIA Boot Agent 253.0543
Copyright (C) 2001-2008 NVIDIA Corporation
Copyright (C) 1997-2009 Intel Corporation
PXE-E61: Media test failure, check cable
PXE-M0F: Exiting NVIDIA Boot Agent

[code]....

Before, I was also getting the error message 'PXE-E53: No Boot Filename Received' prior to the media test failure message. After I unplugged and replugged my internal hard drive (some forums were saying to check the cables for the hard drive) the first error dissapeared.I have a Windows 7 Ultimate 64-Bit OS. I bought the computer second-hand off a guy who was selling it online. He didn't have any of the CDs, so my copy of Windows 7 is burned (though I do have the CD still). Before yesterday it was working fine.All I want to do is to be able to get into the computer (Hard Drive) once, so that I can backup all my files and then I'd reinstall Windows 7 from scratch.