My own preference is for CCleaner from http://www.ccleaner.com/ which flushes out the crap far more efficiently than any of Windows' utilities.
CCleaner is a wonderful system optimizer. But a word of warning, please do not use the Issues
option, as it involves editing of the registry, and one false move and you could render your system inoperable.
Once the program is opened. You should see under the Cleaner Settings
that the Windows
tab is showing.
The one you need to use is the Cleaner
The icon for the Cleaner
will be the top icon on the left hand side.
You may be suprized how much it cleans (removes).
Also as has already been suggested you should Defrag your hard drive and as an added effort run Scandisk.
Start > Programs > Accessories > System Tools > Scan Disk
Start > Programs > Accessories > System Tools > Disk Defragmenter
A Defrag done for the first time may take awhile. Be prepared.
Defrag and Scan Disk are best done in Safe Mode.
Let us know how it goes.