Guilio
A couple of things to try.
1) Locate a file called *.xlb (This file may be hidden and may start with
any file name (Dependent on XL version), but always ends with .xlb). When
you find it move it from it's folder and try starting XL. If it starts ok
you can delete the file. It is Excel's toolbar customisation file and a new
one is created if XL can't find one.
2) Make sure you version of XL is fully patched
3) Run detect and repair from under the Help menu of any office application
(It repairs office not just the application)
4) Finally, try running Excel from Start>Run... and type excel.exe /safe
This will start Excel without loading macros, add-ins etc and if this works
you can uncheck any add-ins from Tools>Add-ins and work backwards until the
error re-appears
--
HTH
Nick Hodge
Microsoft MVP - Excel
Southampton, England
(e-mail address removed)