Do you have a second operating system, you are rebooting to, such as DOS 6.22. If so what op system?
The smaller window you refer to suggests to me that perhaps you are only opening up a CMD window while still running in windows. If that is the case, Right Click the Title bar, click properties, and under the options tab, click Full Screen. After turning on the full screen, it will appear just like the Dos screen that you are looking for. When done type exit to return to windows.
Let us know either way!
I may not be understanding your situation.