The minute your computer's hard disk starts to act flaky, make sure you have an up-to-date backup. Then you can do some simple diagnostics and repairs. Both Windows and Mac OS come with built-in hard-disk utility software that scans your hard disk for errors and attempts to fix them.
Double-click on My Computer to open the My Computer window.
Select the disk that you want to diagnose and repair.
Choose Properties from the File menu. You should see the Properties window for the drive that you selected.
Choose the Tools tab.
Click the Check Now button under Error Checking Status.
Depending on your version of Windows, choose either "Thorough" or "Scan for and Attempt Recovery of Bad Sectors."
Click on Start.
Third-party hard-disk utilities do a more thorough job of diagnosis and repair than the software that comes with Windows or Mac OS, but they work much better if you install them before you have a problem.