bootable usb stick won't boot

[Pedroparamo]

I am trying to make a bootable usb stick for Ubuntu 9.04. I used Unetbootin to laod the ISO onto the stick. When I try to boot from the usb drive my machine gets hung up on the Ubuntu Installer Boot menu (on the usb stick)--none of the options I choose i.e. 'try Ubuntu without changes', 'install Ubuntu', 'check disc for defects,' etc. works--when i chose one nothing happens, my machine just keeps counting down but never boots.

Any suggestions?

Pedro