Delete the following:
Any personal files on the computer from my documents, or wherever you have them. Obviously back them up first.
Temporary Internet Files and Cookies via Internet Explorer
Open a command prompt and issue the following commands to delete temp files:
del "%userprofile%\local settings\temp\*.*" /s /q
Delete Favorite:
del "%userprofile%\favorites\*.* /s /q
Delete Systems Temp files:
del "%systemroot%\temp\*.*" /s /q
Right click Task Bar at the bottom of your desktop and select Properties.
Then click "Start Menu" tab, then Classic Start Menu, then Customize button. Click the "Clear" button on the next screen then click Ok all the way out of all dialogs.
Download "Eraser" from:
Eraser
Run Eraser, click On Demand, and erase "Unused Space". Use at least a 3X overwrite eraqse method. This will take hours probably so just let her rip.
Other route and recommended if you know how:
Format and reload operating system. Then download Eraser and do the same exact steps as to wiping free space.