Take several d-e-e-p breaths then read
this then tell us something about your computer, anything you like, the make and model, what color it is, anything at all but please include the OS you are using and how you get to "my Dos". Is this a new problem or has it been apparent for some time :-? If it's new did it appear after you installed a specific program:-?
Is your OS a version of XP and to get to 'my Dos' are you using Start>Run and entering Cmd or Command :-?
We have great difficulty helping if we don't know what you've got or been&gone&done. Please help us to help you...