Hi I have a basic kindle and I ejected it so I could use while charging, but now can not get back into drive mode.
Using windows XP
You have to physically disconnect the usb cable, then reconnect it... That will tell your computer it is back in action as a drive again. Then you can drag book files to it and all those other good things you can do when it is in "drive" mode.
Be sure to check out The All New Kindle Family... It is amazing what Amazon has been up to lately. You shouldn't have a huge learning curve with these new Kindles... just a lot more fun!