If you do not have Restore Discs that came with your PC, Create them on a CD or DVD set to have for when your computer will not boot. Also create a System Image for the Restore Discs to restore so your PC can be like it was when you took the image.
Think of it this way. A System Image is like a snapshot of your Operating System and Files as it stands when you do it. All your data and programs should be just like you see them but saved on the external HDD for restore at a later point. Anything you add to your computer after you take the snapshot will not be on the backup image until you image it again.
The Restore Discs will allow you to apply the image you took to the installed hard drive and make it back to the way it was before a crash. Generally the built in Windows Backup works fine if restoring to the same hardware and only replacing a Hard Drive. There are many cheap programs out there, around $30 - $60, that will image your Hard Drive and guarantee it will restore to completely dissimilar hardware, say if the motherboard is fried along with the Hard Drive.
Learning - A never ending quest for knowledge usually attained by being thrown in a situation and told to fix it NOW.
