Are you using a damp cloth? I've noticed capacitive screens like the NC useswill stop responding if damp. A quick power off and on usually fixes it. (Just turn off, not a full reboot.)
Are you wiping it clean when the Nook is on? I've found that the rapid random motion of wiping it will "confuse" the Nook, and it's apt to freeze. I just wipe it when it's asleep and all is well.
Search archives for numerous discussions on this issue. The original Nook Color had 8 GB of internal memory on the NC. 3 GB was reserved for system use, and the other 5 GB was ours to do with as we liked. B&N changed that to reserve 4 GB of internal storage, to be used exclusively for content purchased from them. Only 1 GB is available for sideloaded content you obtained elsewhere Your apps are limited to the space B&N had reserved for apps. If you exceed that limit, you must rotate apps into and out of the archives. Unless you convert the original Nook Color to android.
I also have to archive 1/2 of my apps anytime I want to download a new one, why is that?