Hello. I was having the same problem. Turns out that Win7 didn't install the driver just follow the directions on post #31 on this thread
https://www.mobileread.com/forums/sho...=113048&page=3
Basically you need to put the pocketbook in the android_winusb.inf file. Once that is done I went to the device manager, right clicked on the missing device and went to update driver. I had to go through and do a "Choose File" and browse to where that inf file was. Select it and it then installed the driver so I could use adb.
Let me know if you can follow this. If not then I'll try and post a better description.