When Backtrack 5 R1 released and I install it on my notebook the blank screen issue has been disappear, but I found this issue on Backtrack 5 R2 when I install it.
But don't worry, same issue has same solution. The simple thing to do is add some code to the Grub option.
1. If this bug appear when you are using Backtrack 5 R2 Live USB you can press "Tab" button on the boot option menu and this code
vga = 791 splash text" and the press [enter]
2. If you run Backtrack 5 R2 on Live USB and there's no a problem but after you install it this problem annoying you, you can add the same code on the Grub configuration. You can edit Grub configuration on /boot/grub/grub.cfg and find the Backtrack boot menu and add this code
"i915.modeset=1"(same as before) after "
vga = 791 splash text".
I guarantee you that the blank screen should be solved because it's word for me.
If this above solution can't solve your problem maybe you must read Blank Screen Backtrack 5 [NVIDIA] and Blank Screen on Backtrack 5 when Using Startx [Intel]
Hope you solve it