Here's something that drove me mad for a few hours.
I have a 500 GB HDD, and I was trying to clone the primary partition to another with the help of a bootable CD. Well I couldnt, because the boot process kept hanging after reaching the line "loading boot sector......... booting......."
When I searched online forums, I found out that people run into this problem sometimes while booting 911 CD, Ultimate Boot CD (UBCD), BartPE, etc.
There are two reasons why this happens. Well, maybe a lot more, but two that I am aware of! The first one (which I got from forums) is that something is wrong with the way you burned your boot CD. You can check this by trying to boot another system with the same CD. I tried. Mine worked on the second system. I couldnt find any help elsewhere, so I just sat there and kept thinking lol. And I found out that my problem was that I had connected a couple of USB drives to the system. Yep. I dunno why that should be a problem, but if you get stuck while trying to boot at the line "loading boot sector..... booting.....", check if you have connected any removable drives to your system. If you have, unplug them and reboot. It should work fine.