Every workbook????
If you start a new one, save it, close excel, reopen excel and reopen your
workbook, then the worksheet(s) will be protected???? (save the workbook with
the worksheet unprotected.)
If that happens, then try this:
Close excel
reopen excel in safe mode
windows start button|Run
excel /safe
file|open your workbook
Are those worksheets still protected?
If no, then maybe you have a "helpful" addin that's either protecting those
sheets when you close the file (or when you open them (safe mode stops all
macros from running).
Chip Pearson has some notes on how to diagnose startup errors at:
http://www.cpearson.com/excel/StartupErrors.htm
And Jan Karel Pieterse has more notes at:
http://www.jkp-ads.com/Articles/StartupProblems.htm
Essentially, you move all of the stuff out of XLStart and you turn off all the
addins under Toools|addins.
Then you start adding things back one at a time and testing each time to see if
the problem is fixed. When you add something back that causes the problem to
come back, you'll have to decide what to do with that addin.
(Make sure you keep track of all the stuff you turn off and move.)