Hello Mr. R
Start your Excel in Safe Mode by pressing CTRL while clicking on the Excel icon to open it.
Excel will send you a message that you are attempting to start in Safe Mode, click continue.
See if the same issue repeats in Safe Mode.
Close Excel. Restart Exscel normally.
Hope this helps to solve your issue.
Also check a possible solution at Microsoft Office Articles Magazine :
About the XLStart Folder in Microsoft Excel
First, there are really two Excel Startup folders.
One is created by default when you install the application. Its name is XLStart.
The other is created if you go to Toolsà Options, General tab, and enter a location in the At startup.
http://www.officearticles.com/excel/about_the_xlstart_folder_in_microsoft_excel.htm
Hope this helps to find a solution to your issue with Excel. Take care.