You could try sending yourself an email with the link:
file:///c:/
Then navigate to Regedit in the Windows directory.
Or copy and paste one of these:
file:///c:/windows/regedit.exe
file:///c:/winnt/regedit.exe
Navigate to
HKEY_CURRENT_USER\Software\Microsoft\Internet Explorer\Main and change the key "Start Page" to
www.google.com or whatever.