To add to the series How To Clean Your Sluggish Computer…
If you followed every step in the series – How to Free Up Disk Space on Your Computer’s Hard Drive, Speeding Up Your Internet Explorer Browser, Cleaning Hard to Find Problems in Windows Explorer, How to Stop Programs from Running in Scheduled Tasks, and Rearranging and Compressing Files for Increased Speed – and for some reason you want to go back and start all over, you can do what is called a System Restore.
System Restore – System Restore is a component of Microsoft’s Windows Me, Windows XP, Windows Vista and Windows 7, but not Windows 2000, operating systems that allows for the rolling back of system files, registry keys, installed programs, etc., to a previous state in the event of system malfunction or failure.
The Windows Server operating system family does not include System Restore. The System Restore built into Windows XP can be installed on a Windows Server 2003 machine,  although this is not supported by Microsoft. [Source: Wikipedia]
To take your computer back to where it was before you began the clean up process, follow these steps:
1. Close all open programs and files.
2. From your task bar, go to Start – All Programs.
3. Click on Accessories.
4. Click System Tools.
5. Click System Restore.
6. Click Restore my computer to an earlier time.
7. Click Next.
8. On the calendar, click a date that has bold text.
9. In the right table, click on a restore point.
10. Click next.
11. To confirm selected restore point, click next. System Restore will shut down Windows, and will restart after the restoration is complete.
As mentioned in the previous post, if you have followed every step in this series and your computer is still running slow, it may be time for you to consider purchasing a new computer system. Remember to make sure you get someone who is great with technology to help you transfer the files from your old computer to your new computer.
Additional resources: Is This Thing On?: A Late Bloomer’s Computer Handbook