My guess is that something is set to shutdown AFTER a particular task runs. For example, many programs have an option to shutdown after a download. I think uTorrent has this option. There may be a automat shutdown after windows updates too. And virus detection programs may have an auto shutdown option that kicks in.
Suggestion... run Task Scheduler Manager and turn them all off and see if it still wants to shutdown after you reboot and let it run a while. Even easier is to google for a program called Autoruns and it lets you uncheck boxes to disable scheduled tasks. That's much easier that the windows method. While you have it.. see what else is loading when your system boots up. (Be careful with the services though... unless you see something that's not from microsoft Amd, google or another "reputable" company.)
On.. one last thought... press ctrl + shift + esc and see if taskmanager will give you a hint as to which application is showing the shutdown window in the image you posted. If it doesn't, try this... it's not that easy to do.. but if you can watch the "processes" under task manager when you close that window... you may be able to catch what disappears from the list. (That tip should put a gold star beside my name
Most of the time it is from Microsoft Update. They've been downloading, maybe even the previous day and have just finished. They need to finalize and initiate the new programs. Java and Adobe are also the most common. (Usually Microsoft will let you have more time to finish your work, but you have to ask).