When I install Backtrack 5 R3 I came across this problem, but managed to find a fix:
What we need to do is add some code to the Grub file.
If you're using a live CD or live USB you will come across with the below menu, and there you should select the "Default Boot Text Mode" and press "Tab".
You should then, add the following code "i915.modeset=1" to the grub editor after the "vga = 791 splash text" and then press[enter].as
If after installing Backtrack the problem persist you should then edit the Grub configuration file located in /etc/default/grub
Find the line that says:
and add the same code "i915.modeset=1" after the "vga = 791 splash text".
After it issue:
It should be working properly now.
If not, check my next two Fix's.