Try resetting the last used cell.

Debra Dalgleish has some techniques at:
http://www.contextures.com/xlfaqApp.html#Unused

ben@bikecenturies wrote:

I have a 1,000 x 15 straight worksheet with no formulas - about 100K.
I went to auto-format a pattern, but didn't select the area and
if formatted the entire spreadsheet. It's since gone from 5 seconds
to 60 seconds per save and I can't reverse this, even by changing
the auto-format setting to "none."

I'm backed-up, but the current version is about three hours ahead and it
will take longer to retrace the work by hand.

Any suggestions?

Thanks, Ben

--

Dave Peterson