Cursor location jumps automatically
 

What makes the cursor automatically jump from one cell to another in Excel
when trying to change/enter either new/different alphabetical or numerical
data? The data entered can't be seen on the screen in the first or last
cell. I don't recall changing anything in the file (other than saving it)
the last time I had used it. I've developed my own file to calculate my
checkbook for a couple of years and whatever happened appears to have
happened to both that file and another in which I'm keeping home/personal
expense records. The problem seems to affect even new files I've opened
because no new data can be entered in certain rows/columns--the cursor just
goes to the next cell or several cells to the right.