Bob I wrote...
Perhaps updating the video adapter drivers will correct the issue. get
them from the adapter manufacturers web site, NOT Microsoft update.
There are other possible causes. Buttons are just drawn objects, and
Excel allows displaying or hiding them. The first thing the OP should
check is the setting under Tools > Options, View tab, in the Objects
section of the dialog. If either Show Placeholders or Hide All is
selected, change the setting to Show All. Does that fix the problem?
If so, then if there's only one machine with this problem, it's likely
there's a macro on that particular machine that's hiding drawn objects,
which would beg the question how this problem workbook is being opened
- double clicking on an XLS file in Explorer or from File > Open after
Excel is up and running.
If not, it'd be a mystery how the buttons could appear at first then
disappear if this were a hardware driver problem. Also, if the
particular PC in question had different drivers or hardware than the
other PCs, it might also have a different version of Excel, and that
might be another possible cause.