Infinite Windows is shutting down screen.

From yesterday, I have this problem with my Windows 7x64.
It only happens sometimes, not always, but already are 2 times it happens.

In these days, I only installed Windows update 2952664, uTorrent updated itself, Wolfenstein: The New Order, and I downloaded Dolphin emulator, but it hasn't an installation. Just "portable" version.

Any idea what can be?
I use CCLeaner and Disk Cleaner every 2-3 weeks.

Perhaps you can try a clean startup - Troubleshoot Application Conflicts by Performing a Clean Startup

GokAy said:

Perhaps you can try a clean startup - Troubleshoot Application Conflicts by Performing a Clean Startup

Thanks, but I don't see how it can help me. My problem only happens sometimes, and on shutdown.
I mean, if I make a clean startup, 90% I haven't the problem and have to try various times with the shutdown.

Most probably some program or service that is running is preventing the shutdown. With a clean startup, it will probably won't auto start. Problem not happening every time is indeed an obstacle to efficiently tackle the situation.