Like the other user, the Quick Repair did not work, however the online repair popped up two errors, one saying something like "clicktofix.exe" encountered an error an needed to close, and another error window behind it saying something about another installation
was already running. Since I wasn't running or installing anything else during this time, this must be a timing problem in the fix code. Unfortunately, this left me with Office 365 completely uninstalled, including all the setup I did for my start menu.
Something appears to be wrong with this repair code.
It appears that the reinstall recovered the customization I had done on my office apps, including the start menu setup I had performed, but it did not fix the problem. The Excel splash screen remains when launching my xls and xlsx files, with the last message
on the splash screen being "Opening: SOLVER.XLAM. Press ESC to cancel. (100%)". I can move the splash screen around, but pressing ESC or clicking the "X" in the upper right corner does nothing. I can minimize it, but that causes it to drop into a small green
rectangle just above the task bar, which cannot be maximized again. The small box can be moved around, but the only way to get rid of it (or the maximized version) is to close Excel.
I've also tried going into Options and telling it not to display the start screen, which apparently doesn't stop the splash screen, however, I did find that simply going into Options makes the splash screen finally go away. It still appears (and sticks)
the next time I open a spreadsheet, but if I just go into Options, it disappears once the Options window pops up.