You can only leave a USB pen drive in your PC when restarting if you have set the boot devices in the bios. Take out the pen drive, start the pc and go into the bios by pressing the "del" key immediately on start up (just keep tapping the key) Once you get the bios screen you need to go into the menu that has the boot devices, its normally the third one down called Advanced Bios Features. There is a menu at the bottom of the screen telling you which keys to use to navigate around. Look for first boot device and set this to floppy/CD ROM or hard drive you will probably see that one of the boot devices is set as removable this is the one that is finding your uSB drive and trying to boot from it, so change that one first. remember use "enter" to go in and "esc" to come out. Once your finished press "F10" it will then ask do you want to save and exit press yes or "Y". your pc will now reboot inot windows. This is an area of your pc you have to be carefull going into but it will only change the values once you exit and press "y". So if your not sure what you have done press "N" and they will go back to what they were. In this case the simplest thing to do is not leave the pen drive in on start up.