Defragment the hard drive. The built-in defrag utility is fine, though for more advanced tuning (system file defragmentation, free space consolidation etc.) you can look into third-party programs like Auslogics Disk Defrag.
Check the hard drive's SMART attributes with HD Tune or similar program. See the Wikipedia article for a list of attributes, including those that are potential indicators of hardware problems.
Run chkdsk to find and fix errors with the filesystem and bad sectors on the hard drive.