Considerations before reformatting
Backing up files can be a long and arduous task if you have a lot of stuff to save, but the process is quicker and easier than ever thanks to how cheap hard drives and writeable media have become. The easiest method of them all is to invest in an external hard drive with 500GB or 1TB of space. They’re a little more expensive than internal drives, but they connect via USB and can be stored in a safer/separate location. Just plug it in, drag and drop the files you want to backup, and voila! (Alternatively, buy a regular hard drive and an enclosure or other device for USB interfacing.) You can also copy files to DVD or blu-ray, both of which are easier to store than an external hard drive, but it takes longer to burn them than copy files between hard drives and you may need multiple discs to hold all your stuff. Once you’ve reinstalled Windows, just repeat the backup process in reverse.

Viruses are nasty, and sometimes you won’t even know they’re there! Hopefully you have some sort of anti-virus program, but even then it’s possible that something snuck past those defenses and wreaked havoc on your system. If the anti-virus or other anti-malware software was unable to eradicate the bug, reformatting is likely your best and most painless option. You can still back up important files, just be sure to scan them before re-introducing them to your computer later. (Free software to try: Panda Cloud, AVG, Ad-Aware, Microsoft Security Essentials, avast!, Malwarebytes)
If your problem is not caused by a virus, you may be able to fix your problem by simply reinstalling Windows without reformatting, keeping all of your files intact.
A system restore disc can be a boon if you’re having software troubles and just want to turn back time to when your computer was brand new. Basically, it’s a saved copy of everything that was on your hard drive when you first got the computer, including Windows and all of the pre-installed programs. When you boot from it and run the included utility, it will wipe your hard drive and copy everything back on there as if you had never changed anything. Most of the time it’s separate from a Windows installation disc (which may or may not have been included with your computer), but some companies create a custom hybrid disc that can be used for either purpose. You should go ahead and use that if you have one, unless you specifically want a clean install of Windows.

System Restore is a utility built into Windows that periodically saves backup copies of your hard drive and allows you to revert to those saved “Restore Points” at any time. It differs from the aforementioned system restore disc in that it only saves Windows, along with your settings and programs. Everything else is left intact, so even if you use it to restore Windows to how it was a week ago, those files you downloaded yesterday will still be there. It’s a good idea in theory, but I tend leave it turned off because that is usually the first thing to get screwed with by a virus anyway (to prevent you going back to a Restore Point from before you were infected) and it eats up a lot of hard drive space unless you keep up with deleting excess Restore Points. It’s just easier for me to reformat, but if you have System Restore enabled, it’s worth trying to revert back to your earliest Restore Point to see if that fixes your problem.
The self-repair is one of the most useful things included on the Windows disc, but most people don’t even know it’s there. When you boot from the Windows installer, there’s a little link at the bottom of the dialog window that says “Repair my computer.” Clicking that opens up the self-repair utility, which will scan for problems with your Windows installation and attempt to fix any that it finds. This is generally a last-ditch effort to avoid reformatting when the computer won’t boot, probably because you have files that you don’t want to lose. It’s certainly saved me some hassle on more than one occasion, but it’s not a miracle cure. You still have options if it doesn’t work for you, though, which I’ll talk about on the next page.
