I installed Ubuntu to USB ext drive from CD from my desktop, where it boots perfectly from USB Hard drive. However, it does not boot from my laptop. Laptop hangs with a blinking cursor. Can you please help? Thanks.
Did you use USB creator and copied live Ubuntu CD?
Or you installed Ubuntu on the external hard disk and then trying to boot from that disk?
If your answer is first one, then first try to boot your laptop from live CD. If it boots, either bios settings may be problem or you may try again creating USB from live Ubuntu. If it does not boot even with live CD then there may be some hardware issue with your laptop (like unsupported drivers).
If your answer is second one, then hardware configuration of your laptop and desktop must be different. And installed Ubuntu may have drivers for your desktop and it might be conflicting with laptop hardware. This mostly happens with display drivers. Live installation auto detects the drivers and sets them. While installed Ubuntu tries to use installed drivers.
1) check BIOS settings to enable booting from USB-drives
2) make sure a bootloader (e.g. GRUB) is installed on the external boot-drive