There is no prepping required for Android to recognise SD cards. Usually, they work just as thumbdrives on a PC. The "remove hardware" process should be observed because this will ensure that any cached data will be written to the removable media and that the files are all closed.
With Android, in Settings-Storage, there is a Mount / Unmount. This is similar to add or remove the storage media, eg, SD card.
You can try this workaround. As before, when switched off, insert the SD card to the HD7 and then switch it on. Go to the Settings-Storage and you should see the SD card details. Do an Unmount, remove the SD card, wait a while and then re-insert the SD card and do a Mount. You might be able to acess the data on your SD card by now.
If this still does not work and since you had just bought the HD7, bring it to the seller and have it checked. Also bring along both your SD cards that you had tried to use, as well as the Nook so that you can prove to the seller that there is nothing wrong with the SD cards.