Excel- Data I enter appears one cell down from where I attempt to type it in, then will not delete

Ever since I started with Office 365 for Mac I have problems entering simple data on my inventory spread sheets. Right now I am half finished with a new inventory list and all of a sudden any number I enter in a cell appears one cell below?!? Then if I try to delete the entry because it is in the wrong cell I can't delete it.  What is happening?