Alienware M17X R2: black screen of death and won't boot from CD/USB

Hello all.  This combination of problems has me stumped because I'm basically unable to try anything I would normally try. I hope someone can offer suggestions.

My computer's an Alienware M17x R2.

Problems

1. Windows 7 boots to a black screen with a cursor.  This occurs at the point when the login page should appear.  No keyboard/mouse inputs appear to have any effect.  Starting up with F8 and selecting "Repair your computer" has no effect: it resumes the normal booting sequence and takes me to the black screen.

2. Related to this, and preventing me from booting from a Windows rescue disk or an antivirus boot disk/bootable USB, is that my computer will not boot from DVD or USB.  These are read (audible optical drive activity), but then ignored, and the computer boots from hard drive to the Windows safe mode/normal mode menu.  I've tried changing boot order in BIOS and disabling boot from hard drive altogether (this leads to an "operating system not found" message) with no success.

Problem history

I strongly suspect my ATI drivers are implicated in this.  Shortly after installing a driver update, I began having video problems after a particularly nasty video driver crash.  It was in trying to fix these display issues that I rolled back to the latest working Windows system restore point and, from then on, Windows only start as far as the black screen.  (I've seen other black-screen-of-death error reports also starting with an ATI driver.  I won't be buying one of their video cards again...)

I don't remember having booted from CD/DVD/USB before, so I don't know if that problem started then or was already present.

Things tried so far

• Windows rescue disk and installation disk: Fail because it will not boot from DVD.
• Antivirus bootable CD and bootable USB: Fail because it will not boot from DVD or USB.
• 'Repair your computer' from the F8 boot menu: Fails, resumes starting Windows.
• Starting Windows in low-res mode from the F8 boot menu: Still get the black screen.
• 'Last successful boot' from the F8 boot menu: Black screen.  No other options from this menu help.
• Booting to a (Windows 98 era) MSDOS prompt: I can do this (for some reason it will boot from this USB stick), but it doesn't see the hard drive because NTFS.
• Flash-updating BIOS: Managed to do this from the DOS stick.  I updated to the latest version offered by Dell for my service tag, which is [edit: version A10].  I ran the included batch file and the update appeared to complete successfully.  I then looked in the BIOS for a 'legacy boot' option that other help forums suggested would help, but this option is not present.

Computer specs in brief:

• Alienware M17X R2
• ATI Radeon (unsure of model)
• RAID primary hard drives
• Windows 7, all current updates as of a month or so ago
• BIOS newly flashed to latest update available for my service tag, [edit: version A10]

What I'd like:

Basically, suggestions of any options I've missed... especially ways to make it just boot from my bootable media so that I can use the repair options.

I have various backups of my most important data and will reluctantly consider a factory wipe (although I don't seem able to get to this option because of the not-booting).  However, I would prefer to get into Windows long enough to burn my files to DVD for safety's sake.