Give us more info when you can.
Many people have a nasty habit of filling the disk up completely and then they wonder why it fails, that can be recoverable.
But, and this is a big BUT, if the drive is making "clicking" or "whining" noises when you stick it in the caddy then more drastic steps are needed as that means the drive is, or almost is, FUBAR'd. That is when you get an antistatic bag and stick the drive into your freezer for 15 mins. SOMETIMES, that is enough to get the drive working long enough to recover data from it. I don't agree with the "plastic bag and fridge overnight" method as that will introduce moisture to the drive and moisture can be as dangerous as static when you look at the circuit board on the drive. Plus, my method is faster.
Of course, decent data recovery software is a must and, if there is the slightest suspicion of there being a virus issue, so is a "clean" PC to connect to (as in, one that you can easily wipe out should a virus be passed from the dodgy drive to the main PC drive. I keep an old netbook for that purpose).
But I've never failed to get most of the data from a hard disk. It can take some time, as in days, but with the right software and patience (and, occasionally, a light "tap" from a hammer to free the heads. Rough as hell but that works too on a "dead" drive) you can recover the majority of things on the drive.
Oh, obviously, don't just select everything IF you get access to the drive. Windows and other programmes can be reinstalled on a new machine, you are looking at only getting stuff like the "documents and settings" folder and other data that is saved by programmes.