While idling at a website, my computer started making clicking noises which isn't unusual with this laptop. Usually my computer makes clicking noises when the harddrive is in use. However this time the clicking was non-stop so I shut it down. Upon starting, the computer will click and an I/O Error, replace disk and press any key. After pressing any key, the computer will click for about 5 more seconds and the same error message. Any ideas? BTW the computer is about 3 years old