Frequently, cleaning your hard disk manually is more effective than using Disk Cleanup. Disk Cleanup won't find all the files you want to delete, and it might also delete files you'd prefer to keep

A manual cleaning should include the following steps:

• Empty the Recycle Bin.
• Search for all files that end in .bak and .tmp and that start with ~ (use the wildcard * when you searchfor example, *.tmp, *.bak, and ~*.*). Delete them all, except for any files that are dated the current or previous day. You might find some files can't be deleted because they are in use. Don't worry about it; just leave them.
• Delete your temporary Internet files by running Internet Explorer and choosing Tools > Internet > Options > General > Delete Files.
• Delete files in your \TEMP folders. There might be two of these folders: one named C:\TEMP and the other named C:\Windows\TEMP.
• Delete old system restore points, which can take up a substantial amount of space. You can delete all your old system restore points except the most current one, so before doing this, make sure you don't need any old points. Run Disk Cleanup, then choose the More Options tab and click the Clean Up button in the System Restore section.