The Windows 7 installer to burn to DVD or write to flashstick is provided in Step 1 of Clean Reinstall - Factory OEM Windows 7
What I would do is rescue your files if necessary as also shown in the tutorial, then from the booted DVD with everything else unplugged do a Custom clean reinstall following the steps in the tutorial closely.
In particular you'll want to delete all partitions as shown in Steps 6 and 7 of Clean Install Windows 7
then create partition(s) as you wish, or just click Next and Windows 7 will create and format one large install partition (as well as a small boot partition you can ignore).
Melissa it's important to read and understand the steps involved closely. Feel free to ask back any questions until you understand everything thoroughly. If you get the install perfect with our help, then you can save a backup image to use in place of future reinstalls, so you only need to get it perfect once.