1. First, run a scandisk or checkdisk. Let Windows fix any errors.
2. Run a disk cleanup utility...this will flush your temporary internet folder, trash can, temp system files, etc.
3. Delete any garbage files or data...if possible, run a Duplicate File Finder program.
4. Run Defrag on all partitions (NOTE: run this after you have deleted all trash and excess files!)
5. Run a registry cleaner