Recently I had BT5 R3 installed on a Dell Latitude laptop, and it was working fine. Then I needed to clone the hard drive, so I used DiscCopy 2.3 to copy the drive--No issues.
However, when I went to boot back into my BT install, the screen was all messed up immediately after it hit the splash screen. I couldn't figure out how this happened, as I didn't mess with the OS at all (I copied the drives outside of the OS, booting to the DiscCopy CD).
Initially I was worried I had a hardware failure, so to test it I booted into the original Windows 7 Drive that came with the laptop (when I installed BT I set that drive aside, as I don't normally use Windows). Windows 7 booted fine--no hardware failure.
However, when I booted to a BT instance I had happened to have installed on that same Windows 7 hard drive, a drive that was cleanly working when I put it in storage, it had the same video problems!
So my symptoms were that I had a video problem with BT only, that spanned across hard drives! How the heck was that possible I wondered? Turns out it was my FrameBuffer. This is a hardware device that renders the graphics for the OS--thus it is hard drive independent, which explains why I had a problem that persisted across hard drives, and even with the BT bootable iso!
So to fix this, I booted the BT bootable iso, but into "noDRM drivers" mode. This allowed me to actually boot the previously unbootable BT iso, and mount the hard drive. I then edited the /boot/grub/grub.conf file to say "vga=normal nomodeset" The 'nomodeset' is key, as it told the OS not to load the framebuffer.
I booted up, and Bob's your Uncle---BT is working again!