I have installed Ubuntu 13.10 on my pendrive. I have Windows 7 installed on C drive of my hard disk. When I start the computer without connecting pendive to system I am getting this error message 'No such device. Entering rescue mode'. But if pendrive is connected to system while start up everything works fine, I get a screen where I can choose OS. Is there anyway that I can keep Ubuntu on my pendrive and use it whenever required without having it be connected on every system startup.