Few hardware failures cause more headaches than a dead or dying hard drive. Other components, like videocards and RAM, result in lost time and inconvienence as you wait for your RMA to process, but when the replacement arrives, you're back up and running as if nothing happened. But when your HDD goes bad, you're not only looking at downtime, but lost data, like Word documents, emails, pictures and videos, saved game files, browser bookmarks, and that snazzy wallpaper that you can't remember where you downloaded it from. Fortunately, hard drives rarely conk out without any warning, giving you both a chance to detect impending failure, and to extract any important data that might not already be backed up.
A more subtle sign comes in the form of file errors, and you may receive warnings from Windows that you need to run the check disk utility. If after doing so you continue to meet head on with more errors, your hard drive may suffer from bad sectors.
Other signs include unusually slow access times, incomprehensible files names, crashes, and other undesireable behavior. If you're experiencing any of these, or the ones previously pointed out, backup your data immediately and then begin the diagnostic process.
Faulty hard drives can result in all kinds of goofy symptoms, some of which prevent you from booting from the drive altogether. I had one incident where a hard drive of mine all of sudden decided that it no longer utilized the NTFS file system, and instead was formatted with FAT16. I couldn't boot into Windows, and because I was naughty with my backup routine, there were several files I wanted to extract, if only I could access them. Thankfully, I was familiar with Quetek's File Scavenger program. It's not free, but at $49, it's far less expensive than professional data recovery services, and in the times I've used File Scavenger, it's been highly effective. And you can run it from a memory stick or CD.
If your hard drive refuses to be recognized and you strike out with data recovery software, there's still a chance, albeit a small one, that you can gain access long enough to extract data. Many users have reported some success with the freezer method . As off the wall as this sounds, you put your hard drive in a zip lock bag and throw it in the freezer for at least an hour. When you take out your digital popsicle, wipe away any condensation and install it normally. Your success will vary, and if it does boot, you may only have a matter of minutes before it dies again. Some have had success with freezing their hard drive a second, or even third time.