This is the one of the strange issue when you are working with sharepoint.
For me this error occured on of a sudden, last week. It took 2 days to find a resolution for this error.
Finally got the solution today.
I am not able to browse my web application and trying to find the root cause of the issue finally i figured out that User Profile Service synchronization is stuck on starting.
User profile synchronization service stuck on starting as below
Basically sharepoint user profile service is dependent on active directory and lot of other stuff. Managed meta data service is one of them.
When managed metadata service and user profile services run on paralally this will cause a dead lock situation.
Because of this Forefront Identity manager service might be disabled as shown below
Solution :
Below are the resolution steps for this issue :
1. Delete the User profile service from CA
Open Central Admin -> Click on Manager Service Applications -> Delete the User profile service
2. Configure and start the managed metadata service
3. Re configure the user profile service
4. Start user profile synchronization service
5. Restart IIS Service
NOTE : Step 2 and 3 are optional if you really using Managed metadata service
Thank you !!