Just came across this – if you hold CTRL while opening MS Excel, it will ask if you want to open it in Safe Mode.
It would seem that when opened in Safe Mode, Excel does not load its files and add-ins.
Details of Excel in safe mode and other ways to open it in safe mode are available at the following links:
http://excel.tips.net/Pages/T003365_Starting_in_Safe_Mode.html
http://www.pcpowerguide.com/windows/office/starting-microsoft-excel-in-safe-mode/
