Sometimes you just want to go back in time. While in life, that's not usually possible, Windows is a different story: System Restore lets you take your PC back to an earlier point in time, letting you restore your PC to an earlier state, in which programs and settings revert to the way they were in the past. Of course, the main reason for doing this is that you installed something that messed with the smooth functioning of the PC, and your aim is to restore the PC to a condition in which it runs well.
If your goal is more drastic — namely that you want to clean out or restore the computer to mint condition — Windows 8 has built in tools for this. I explain these in A guide to refreshing or resetting your Windows 8 PC. Just one update to that article is that in Windows 8.1, to get to these options, you go to Settings, and then choose in Settings > Update & Recovery, and then you select Recovery. From there, you use the Refresh and Reset tools as described in the earlier article.
But if you do indeed want to restore to an earlier state, the most important thing to know about restoring any Windows PC is that you need something to restore it to — a restore point. To create a restore point, you can see my article How to set a Restore Point in Windows. By default, Windows' System Protection feature automatically creates restore points after system updates and program installations. To make sure of this, got to Control Panel and navigate to System Properties > System Protection, and click the Configure… button. The top choice in the resulting dialog shows whether System Protection is on and lets you disable or enable it.
One important thing to know is that System Restore doesn't affect any of your documents, photos, or other personal data files.
So, assuming you've got a restore point to work with, here's how you restore your PC to an earlier state:
1. From the Windows 8 Start screen, type "Restore." The top result in the right-side Search panel should be "Create a restore point." Even though that's not what we're doing today, that's the choice you want to make. It opens the Control Panel to the Systems Properties dialog's System Protection tab, shown below:
2. Tap the first button on that property sheet: System Restore. This opens a wizard-like dialog, the first page of which says "Restore system files and settings" as shown below:
Here you get another chance to see which programs will be lost and gained. Tap Next.
3. Then you'll see a dialog with a choice of system restore points, like the one below.
You'll probably want to choose the most recent one, so that you don't lose too much in the way of new updates, programs, and settings. If the PC isn't fixed after this restore operation, you can always restore back to an even earlier one. Another helpful feature is the "Scan for affected programs" button. This will show you everything you'll lose by reverting the PC to the earlier state. It also displays the informative message "Any programs that were added since the last restore point will be deleted and any that were removed will be restored." You might want to make a note of the software in this list, in case you want to do some re-installing and uninstalling of wanted/unwanted programs.
4. Hit Next. Now you'll see the "Confirm your restore point" dialog, which lets you do exactly what it says. Note that you can tick the "Show more restore points" box to do just that. You're also prompted to save any open files and make sure your Windows Password works.
5. Click Finish. You'll then see a final warning dialog telling you that once started, the System Restore cannot be interrupted, with another confirmation button for continuing the process. Click Yes.
6. Next you'll see a progress timer saying Restoring System, after which a Windows Update-like screen will pop up full-screen, saying "Please wait while your Windows files and settings are being restored." The process will run through initialising, restoring the registry, and then it will restart.
For my test PC, which didn't have much installation and update history, the whole process only took a couple of minutes, but of course if you have installed a lot of software since the date of the restore point, you can expect the process to take longer. Fortunately, despite the password warnings, I could still log into my test PC with my four-digit PIN. Note: this may not work if you've upgraded to the Windows 8.1 Preview; it didn't for me.
After the procedure, you'll either see a message saying that the restore operation was a success, or one saying that it failed. In either case, but especially in the latter, you can undo the restore operation — you see, Windows creates another Restore Point right before the operation. You can undo the restore operation the same way you start a restore, using the steps above.