Check the spelling. If it is ok then it means startxfce4 is not in your path, or not installed.error message is that there is no starxfce4 command.
When using startx please direct output to a file to investigate why it failed.
startx 2>/mnt/debug
You can also get useful info from /var/log/Xorg.log
If it sticks on a black screen after startx try this as a start script:
Code: Select all
startx 2>/tmp/debug &
sleep 10
pkill startxfce4
killall X