Thank you for your post.
At the time Instant Web Publishing would no longer turn on, do you recall any changes made to your system?
Do you have any plugins installed?
What other applications are concurrently running? Have you tried this without other applications running?
Try running "msconfig" and stop all non-Microsoft services.
Do you have FileMaker Server installed on the same machine?
Create a new user account, log into the new user account, launch FileMaker Pro 10, create a new database file and try turning on Instant Web Publishing.
Any other information you can provide about your system may be helpful.
If you found a solution, please let us know.