make sure your usb is mounted, it won't be if the usb wasn't plugged in before bootup, if it isn't do this:
cd /mnt
ls
#if there is no sdb1,sdc1,sdd1, or sde1
#then
mkdir sdb1
mount -t /dev/sdb1 /mnt/sdb1 #if that doesn't work, then try
mkdir sdc1
mount -t /dev/sdc1 /mnt/sdc1 #if that doesn't work, then do sdd1 or sde1 ,etc, I'm sure there's an easier way to see which device the usb is tied to, but I don't know how yet, so just do that
then do(replace the sdb1 with the correct one)
cat /etc/X11/xorg.conf > /mnt/sdb1/xorg.txt
umount /mnt/sdb1
then post it up here
p.s. READ THE SLACKBOOK, google is your friend
I recently had the exact same problem from both my usb and my live cd trying to run bt3.
I downloaded bt4 beta and made a live cd and it worked flawlessly.
Then made a USB version using UNetbootin and been working fine ever since.