OK, according to the system info I have Excel version 11.0 build 6560.
This seems to be the latest version.
The workbook size is 5577.5KB.
It has 37 worksheets.

Yesterday I lost the ability to edit directly in a cell in one sheet,
but the "edit in cell" option is selected. I can edit in-cell in all
other sheets.

The thing is the mouse scroll wheel doesn't scroll the sheet, even if I
use cursor keys the sheet doesn't scroll. I can't use "pick from drop
down list" anymore. Excel even gave me a graphics bugs yesterday as the
cell bounding box went all over the place except around cells and the
sheet looked like the video card's memory was faulty. I should have
print screened it...

I have a bad feeling that the workbook is somehow corrupted and will
eventually no longer function properly. It is a huge inventory system
and it would be a nightmare to lose the latest changes to the system.

Is there a "db doctor" kind of tool to check for weird stuff in excel?

I will try to copy the whole sheet to a new book and copy it back, but
this scares me, is Excel flaky or what?