If it's a factory-built PC there should be a manufacturer's utility which allows you to make a set of recovery discs (several blank DVDs are required).
If it's not a factory-built PC you need to use disk-imaging software and a second hard drive. There's a system image creator- built in to Windows 7: Control Panel >> Backup & Restore >> Create a system image
Third-party software is better though If you want to back up every partition including any that aren't required for Windows to start.