I believe I've solved my own problem:

I'm currently using an ATI X700 graphics card with dual monitors, running
ATI's dual monitor management software - Hydravision. It seems Hydravision
does not like Excel's chart drawing. I think Hydravision listens to windows
drawing events so that it can reposition windows and draw its own min/max
icon next to the standard min/max icon. To solve this problem with the screen
going blank/white, I added Excel to the exclusion list in Hydravision. Its
too bad I have to do this, as the Hydravision softwared is handy when viewing
multiple spreadsheets in a large Excel window that spans multiple monitors.