Restore Point

A restore point is, in my words, the younger brother of a backup. It's function is to "keep you on the safer side". If you set up restore points, customizing will never be a risk. Many advanced customizations edit your registry, explorer, etc. These are very important core features for your computer and any problem with these might completely mess up your computer. So, you should always set restore points before doing anything "serious".
To set up a restore point

1. Open System
2. In the left pane, click System protection.If you are prompted for an administrator password or confirmation, type the password or provide confirmation.
3. Click the System Protection tab, and then click Create.
4. In the System Protection dialog box, type a description, and then click Create.

For information about repairing you PC using a restore point, click here.