Yesterday morning when I started working, I found that my app was not able to access the database. I opened up SQL Server Configuration Manager and saw that SQL Server and SQL Server Agent were both shut down. I started them manually and went about my day.

This morning the same thing happened and I remembered that last fall I had had a very strange (similar) problem that took weeks to solve and had something to do with updates. Looking in Vista's Installed Updates History, I could see that there had been two failed attempts in the past two nights to install Security Update for SQL Server 2005 Service Pack 2 (KB948109).

I ran the updates manually and it succeeded this time.

Out of curiosity, I looked at the blog post from last fall Mystery of the SQL Server 3am shutdown and the scenario was exactly the same. Back then it had also been a security update for SQL Server Service Pack 2, just a different KB (934458).

It was lucky that I happened to remember the problem (and solution), but smarter for me to blog these things even if it's only for me to help myself with at a later date. :-)