Have you ever been working on something only to have another app try and abruptly shutdown or restart your computer? If that sounds like something you’ve encountered before I recommend taking a look at ShutdownGuard.
ShutdownGuard tries to prevent apps that initiate a graceful shutdown of your machine without your approval. If you are using Vista or Windows 7 you should see a screen similar to the one above when that happens indicating that ShutdownGuard has prevented the system shutdown from going any further. It then gives you the ability to cancel out of it.
The only downside is that this can’t prevent every shutdown. Some apps may tell Windows to forcefully shutdown regardless of the response returned by any other running programs, and those apps will win over ShutdownGuard.
ShutdownGuard Homepage (Windows only; Freeware; 32/64-bit)