Right click the shortcut on your desktop and select properties. In the shortcut tab add a space and _P on the end of the target. Save the changes and restart Thunderbird to open the profile manager.

EDIT that should be -P not _P

Thanks for the help but the program refuses to open the back up folders for email etc that I painstakingly set up and kept up to date on another drive so it looks like I have lost everything

backup... exactly what is in this backup, and how do you expect Thunderbird to open it. I assumed if your trying to open it that it is a complete backup of your profile. If it is something else then You best explain what it is you backed up-.