Hello, I found three useful software for cleaning up my computer and want to share the experience with everyone.

1. CCleaner 1.26.218
2. TweakNow RegCleaner 2.6.7
3. Abexo Free Registry Cleaner 1.0

1. CCleaner 1.26.218
"...Although it lacks a few features found in other PC-cleaning applications, this free program offers enough to make it a worthy download. The interface is logically designed and makes it easy to wipe away your tracks from Internet Explorer and Mozilla, various Windows system areas, and a few third-party applications. Although CCleaner doesn't support a large number of extraneous programs as some competitors do, it can erase traces from such popular programs as Spybot - Search & Destroy and WinZip. This application lacks a secure file shredder, but it makes up for the omission by supplying a Registry-cleaning utility, which quickly scans for invalid entries before removing them. CCleaner even can back up your Registry before removal, in case it accidentally removes a crucial component, and includes a feature for uninstalling any program on your machine. Since this free application handles the majority of PC-cleaning chores and offers a nice extra, we have no problem recommending it to all users except those who need to get rid of supersensitive data....."
- from download.com

2. TweakNow RegCleaner 2.6.7
"...The Registry is the heart and soul of any Windows system. It contains information that controls how your system appears and how it behaves. When you install an application, new Registry entries will be created. These entries automatically will be deleted when you uninstall the application. Unfortunately, this process does not always work. Sometimes, some applications fail to remove their own Registry entries. These entries become obsolete. After a long period, after you install and uninstall a number of applications, your Windows Registry will contain a large number of obsolete entries. This will significantly increase the Registry size and slow down your computer, because Windows will need more time to load, search, and read data from the Registry. To keep your computer at top performance, it is recommended you periodically clean your Windows Registry.

Version 2.6.7 may include unspecified updates, enhancements, or bug fixes....."
- from download.com

3. Abexo Free Registry Cleaner 1.0
"...By time Windows registry gathers a lot of invalid entries that cause system complications and slow down your computer significantly. Included in Complete Registry Cleaner is a registry defragmenter also called compressor, which removes the empty spaces after a cleanup and thereby reduces registry size. Registry defragmentation increases the performance of your computer dramatically. One-click registry back-up, clean-up and defrag. ...."
- from download.com