It all depends on how your OS came to be installed on your machine. If you have an OEM version that came pre-installed then there should be an option or piece of software provided by the manufacturer to create recovery disks.
Look at the licence sticker that should be somewhere on the machine, it will tell you whether you have an OEM version or a retail version.
If you have a retail version you can download the relevant ISO from http://www.w7forums.com/threads/official-windows-7-sp1-iso-image-downloads.12325/ and burn it to DVD or create a bootable USB. One thing to mention, though, is that you cannot download a retail version of Windows and use an OEM serial key.
If you have no sticker then it indicates that your OS is pirated, as...