Installing Ubuntu on USB not working now! sad :(

Earlier i installed ubuntu 14.04 on my pen drive but something went wrong and i had to format it and reinstall but now when i did,although the whole installation process gets completed but when i try to boot through the particular pendrive on which ubuntu is installed, the screen gets black with the cursor blinking and nothing else…Well although i’ve installed ubuntu on my desktop but i wanna to have on my pendrive as well but now this issue is quite disturbing…someone help please…thanks in advance…

but I installed my external hdd. and it works. but not in all notebooks.