Hi again!
Please start with backing up the registry. How you do that, is described here: http://pcsupport.about.com/od/windows7/ht/backup-registry-windows-7.htm
Then, please create a restore point. How you do that, is described here: http://windows.microsoft.com/en-us/windows7/create-a-restore-point
Now, you can safely try to find the registry-entry.
Type regedit in search in start-menu and choose regedit.exe by clicking on it.
Now you are in the registry-editor.
On the left side under Computer, click on the little arrow next to HKEY_CURRENT_USER for expanding a list of items. Search for Software and again expand it by clicking the little arrow beside it. Now look for Microsoft, expand it again and search for Windows. Expand it and look for Current Version. Expand it and look for Explorer. Expand it and look for Startpage2.
Note: on the bottom of the window, the following path should now be displayed: Computer\HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\StartPage2
Now left-click on StartPage 2, and search for Favorites in the right side of the window. Click and choose delete for all values beginning with "Favorites".
Now, your StartMenu should be empty, and you can start pinning whatever you want there.
I hope this helps!
Cheers
Julia