The hard drive, the single most important component in any computer or laptop.  Everything in a computer can be replaced or repaired including the hard drive but its what is on the hard drive that you can't get back. The hard drive is where every single bit of data is stored.  All your music, photos, programs, documents, spreadsheets, quick books files.  They all reside on the hard drive.  It's not a question of if a hard drive is going to go bad but when.  If your computer is running extremely slow and your anti-virus isn't detecting anything then in all likelihood your hard drive is dying.