Missing all info above the grid box

Q-1: it happens in every workbook - file

Q2: When I open Excel, I seen the "normal" opening page as shown on the attached screenshot. When I open ANY FILE I ONLY SEE a "grid", the top of which is
the "column headings" ribbon showing column headings A B C D E etc.,.............and the right side of which is the "row headings" ribbon showing
from top down, 1 2 3 4 etc. exactly what is shown on my two previous screenshots.

Q3: the IS NO "MAIN EXCEL WINDOW" - only the "grid" I've described.

Q 4: If I understand you right, YES, they are "on their own. NOTE: when I have an open excel window (grid only), when I click on the "+" at the bottom to the right of "Sof the
screen, it moves to "SHEET 1" - it moves to "SHEET 2", etc. and each of those sheets are identical to the previous one (except of course, they have no writing/numbers like
SHEET 1 has.

NEW QUESTION: All of my files are either in the 2004 version or the 2016 version. You can see that on the Opening Page screenshots where some file icons
have a "dark background white X" = 2016 version, and "white background dark X" = 2004 version.

Is there a way to somehow "convert" every old version file to a new version file ??????????

Thanks for any help.