I have a SQL Server 2005, whose tempdb grows to 19.6G (which is very large in my case). I tried to shrink it, but failed. Although no one is using this database at that time, I still can't do it. I've met this case on other database: the database can't be shrinked but no one is using it.. Can anybody tell me why?

Since the shrinking dosen't work, I restarted the instance to solve the problem. However, after that, I found the tempdb is still 19.6G. And reading from the errorlog, I found that the tempdb is been restored automatically!! Luckily, this time I can shrink the datebase. I believe the tempdb is been deleted and then created each time the instance is been restarted. So I'm wondering about it.