There IS a lot of fragmentation going on in a tiny section of my
HD. In answer to your question  on my software, it's Windows XP 5.1
2002, Office 2003 SP-1, 500+ MB RAM. But it's not the real Windows
(ref. my newphew). In answer to your question on .png's--YES I've
removed them, and have removed every downloaded one from every place
in file  storage that I could do. I've replaced .png with .jpg.

The puzzle is, that the problem began it seems with download of lots
of .png (portable network graphics)clip art into successive sheets
of my workbooks (majority of clip art were directional arrows, &
it's a sane project) until everything crashed. Now after removal of
all .png, the crash problem continues only on my largest sheets as I
attempt hefty edits.