Sounds as if you have a drive letter conflict, and possibly a duff usb pen drive (these are cheap as chips, so a new one won't cost the earth)
For your DVD drive try this:
Open device manager from control panel.
Scroll down the list until you find the entry for the drive in question.
Right click the entry and choose "Properties"
Delete the device and then re-boot (Windows should find, re-install and allocate the correct drive letter)
I'd be inclined to bin the dodgy usb drive and get a new one if this works.