IIS does not work after TFS installed

Hi,

I have a problem about IIS for a few days, and i tried a variety of solutions from the websites. But couldn't solve the problem.

After my friend installed TFS server, all the websites on IIS don't work anymore. We get the error"Service Unavailable. HTTP Error 503. The service is unavailable." Before TFS installed, there had not been such a problem.

- Firewall is closed.

- We tried to restart Application Pool. (.net 4.5)

- And tried another Application Pools.

- We gave all the permissions for IIS folder.

But nothing changed, we're getting the same error.

Please help about that, we couldn't solve for days.