The same thing has happened to me!
I've spent about 8 hours trying various 'fixes' - none of which have worked.
What is so annoying is that this issue has been arising with Vista and SP1 for literally years!!!
I'm about to:
1) Scream
2) Use a Linux rescue disk to save all my important data
3) Reinstall Vista - if it will let me...
4) Find out how I can use Linux with a Tablet PC
5) Put it all down to experience