While not specificaly a exchange issue but could be on a Exchange server.
Had a situation where the WWW service was missing even after re-installing IIS.
Turns out there was a Group policy that changed permissions on the registry and did not allow the install.
- Go to HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Svchost
- Give full control to the administrators group on the SVCHOST key
- Un-install WWW service only
- Re-install WWW service
Now the service should be there and running