A bug in my Office 365 Excel?

For some reason Excel pings and then blanks out the whole of the ribbon when I try to copy and paste a  data to overwrite previous data - eg 2 columns by 72 rows - not a great deal of data I would have thought.  I am using Office 365 on a PC.  I haven't figured out what to do to fix it.  Any advice would be appreciated.  It is driving me nuts!

Thanks