if its a Dell shut it down, press the power button and immediately start pressing F12, when you get to the menu look for on board or hdd diagnostics and press the corresponding number. It will give you a message stating the diagnostics are running please wait. It will also give you a HDD model code, Write it down and when the test is done it may give you an error code 1-8. Write that down as well and call Dell at 1 800 624 9896 and enter your express service code (all numeric code on a sticker on your system) and have it replaced if its under warranty. Normally youll get an error code 7 which is a read write error. If its not a Dell call your computer mfg and ask them if they have a diags you can run and see if its under warranty and if so run the diags and replace if it fails!