You can always re-install your Windows 7 even if you don't have the DVD. Just download the Windows 7 ISO OEM online (which does NOT contain any keys) and use your Win 7 key that came with your computer.
Note you have to match versions so if you got Home premium, you will have to use the home premium install on the Win 7 ISO. Note the windows 7 OEM ISO you can use wither 32bit or 64bit OS install.
While that will work, there is a much simpler way that will restore your windows 7 AND ALL program - FREE.
Just go into windows 7 control panel and select Back-up. Then create a sytem image of your "C" drive (Will also atuo include that tiny 100mb partition). Store it on (a) USB HDD or a 2nd internall HDD, or Select to Put it on DVD(s). You can also make a bootable restore disk, or as I do any old windows 7 installation disk will restore this image.
PS THIS is a Excellent idea just incase you have a HDD crash.