I need help with PC DOS issue

My PC crashed some days ago, and I was able to get a Windows 7 DVD.in order to repair windows as was recommended. But everytime I try to boot from the DVD, it comes up with the DOS program. It shows something like:

MSCDEX Version 2.25
Copyright IBM Corp. 1986-1994. All rights reserved.
Drive C: = Driver MSCD001 unit 0

IBM Personal System/2 Mouse Program
Mouse Driver installed successfully
A:/>_

Then every command I type into it, it says bad command or filename.

What can I do? The primary drive is A: in this case while the DVD drive is C:

You must have gotten a bad copy of Windows 7 install media.

Go to the thread linked below and download another copy. Use the key that you already have to activate Windows 7.

Windows 7 ISO – Official Direct Download Links

Are you sure your computer is actually booting from the DVD? In your BIOS you need to make sure your DVDRom is first in the boot order.