Q: Iphone 4S keeps asking to reactivate

My mom's iPhone 4S was working fine until she went to use it a few days ago.  It will let her use her 4 digit password, but then the phone opens to a screen asking her to activate the phone.  It will not let her get out of this screen and only gives her options of emergency call and wifi settings.  I was afraid to go through with activating the phone, since I do not want her to lose all of the pictures that she has stored on it.  Has anyone else had this problem?  Help would be much appreciated!!