Here's how to create a restore point.
  1. Click the Start  button, then select Control Panel > System and Maintenance > System.
  2. In the left pane, select System protection.
  3. Select the System Protection tab, and then select Create.
  4. In the System Protection dialog box, type a description, and then select Create.

To restore your system, including the registry using System Restore simply open System Protection again by following steps 1-2 above and clicking the System Restore button to launch the System Restore wizard.  Follow the onscreen instructions and select the most recent restore point that you created to restore your system and settings from that restore point.

If your PC will not start you may use System Restore offline from the repair settings menu which you should be presented with during boot once the system fails to start.  Again, once the System Restore wizard starts simply select the most recent restore point you created to roll your system back to that restore point.

Backup your Registry using Registry Backup

  • Download Registry Backup from here and save it to your desktop
  • Right-click on the ZIP file you downloaded and select Extract All...
  • Follow the onscreen instructions to extract the files to a convenient location such as your desktop, leaving the checkbox next to Show extracted files when complete checked
  • Once it finishes and you're viewing the extracted files, open TweakingRegistryBackup.exe and click Yes if prompted by User Account Control
  • Once it opens, click Backup Now at the bottom

If you need to restore the registry later on simply run the program again and this time select the Restore Registry tab and use the drop-down menu next to where it says Select Backup To Restore (#).  You can either restore the entire registry from your backup(s) or you may select specific registry files (hives) to restore; if you aren't sure what to choose simply use the default option to restore all of it.  Once you're ready, click Restore Now at the bottom.  Once you restart your PC your registry will be restored.

As for how to do what I was referring to, you must open regedit.exe and navigate to HKEY_LOCAL_MACHINE\SOFTWARE and look for folders for programs you've already uninstalled from your PC.  I can't really help you out on this part as I have no way of knowing what software you've removed from your computer in the past so the only advice I can give is to be extremely careful to make certain that the only folders you remove belong to software that you no longer have installed on your PC.

Once you're done there you may do the same for the folders under HKEY_CURRENT_USER\SOFTWARE.

A good basic tutorial on getting started with the registry can be found here (you'll notice that at the bottom of that article they share a very familiar opinion of registry cleaners ;) ).  Microsoft also has good resources here as well as here and here.  While some of those Microsoft resources are for Windows XP, they still apply to newer Windows versions as well.

Anyway, I hope you find this information helpful, and just remember to use caution.  It isn't worth breaking any of your software or rendering your system unbootable for the sake of removing a few orphaned registry keys/values, but if you really want to learn, this information should give you a good foundation.  Just be cautious and take it slow, and even better, if you have an older system or a virtual machine you can practice on that you don't care about, that would be most excellent as that would take the pressure off and give you the chance to really dig in.