It could be a virus... Check your startup as 2cents says, run TDSSKILLER and Malwarebytes Anti-Rootkit, GMER and even run ESET Sirefef Removal tool. all easily googled.
Sometimes, an MS Update will show a DOS Box when booting, or when it gets to the Desktop after rebooting. Usually this is only once.
If this happens every time, then in it something scheduled to run. I can't see what it looks like, the image is too small or is not the right kind of image.
Sometimes a computer will have a task scheduled left over from a Virus, even after the virus is removed, the task is still there and it tries to run a command line, if the items listed in the command line are not there anymore, then you may get a box like this on startup.