If you are facing some difficulty loading Windows 7 operating system. The if you would like to reinstall Windows 7, you need to have your Product CD / ISO Image and the Serial Number to activate the product once you have installed.
Even if you miss any one of these, you will not be able to successfully complete the Windows 7 Installation. Which means that you cannot restore your PC.
In such case the first thing you need to do is to read the manual that came with your PC – “the part about Recovery options”
If you have the product key alone without the installation disk, And if you would like to reinstall Windows 7:
If the computer is from OEM with Windows 7 pre-installed, you can contact OEM to order a disk for installation.
If you purchased Windows 7 from retailer, you can contact Microsoft Customer Service to order the disk.
Microsoft Customer Service (800) 426-9400 is available Monday through Friday, from 6:30 A.M. to 5:30 P.M. pacific time.
Microsoft Customer Service mainly handles issues regarding replacement manuals, disks, drivers and service packs, product IDs, or lost CD-keys, product orders, policies related to copying software on additional computers, licensing, and product registration.
Here are information for system recovery.