Given so little details I can only write you should learn to use a LiveCD such as Ubuntu (see google) to get your files out. Read http://tips.oncomputers.info/archives2004/0401/2004-Jan-11.htm to see how we began doing that years ago. Today this is even easier.

Since we don't know which Vista DVD you have any advice is nothing more than a guess you could do that. For example once your files are safe and if it's like the Dells we have you can perform a "Vista Repair Install" (see google.)

Good luck,
Bob