If you ever have trouble starting Virtualcenter check the logs.
C:\Program Files\VMware\Infrastructure\VirtualCenter Server\Logs
Look for this message:
[2008-01-17 01:05:43.917 ‘App’ 304 error] Unable to get exclusive access to VC repository.
This means there are some connections to the virtualcenter database (repository) that need to be freed before virtualcenter can use it. It will not start until it can get this exclusive access.
You can either restart the entire database server or locate any connections to the database and terminate them.Â Then restart the virtualcenter service.