What you have there is a WD Scorpio Blue drive in the 500GB flavor, model number WD5000BMVU. The controller board on it is known for being problematic. Your drive has a twin with a SATA interface instead of the USB interface, WD Scorpio Blue model WD5000BEVT.
Your data is on the HD platters, it isn't going anywhere. As you have defined the situation. The hard drive doesn't spin, isn't recognized by the computer. If I am wrong on my surmise of the situation. Try data recovery programs prior to following my suggestion.
You need to acquire another hard drive with one of the previously mentioned model numbers. If you turn your hard drive over you should find screws attaching the circuit board to the hard drive. You need to remove the screws and slowly, gently lift the board away from the hard drive. Pay close attention while you are doing this because there maybe a delicate ribbon cable coming from the hard dive and attached to the controller board. You need to release that cable if one is there to remove the controller board from the hard drive. You need to repeat this process with the newly acquired hard drive. Then take the good controller board and attach it to the one that has your data. If the reading heads made it to their parked position not only will your hard drive be recognized but your data will be fully accessible with out the aide of a data recovery program. If the heads didn't make it to their parked position your drive will be recognized by the computer and it may say the HD needs formatted. Don't pay attention to that and do not format it. A good data recovery program will find your information anyways. If you need to use a data recovery program you will also need enough free space on a hard drive to move the data over to.
I have done this successfully several times. I've never had a time where I tried it and it didn't work. I have done it with western digital hard drives, never with your model of hard drive.
Several people here have mentioned data recovery programs. I am not an Apple person. If your operating system was Windows I would recommend several to you. If you do have to use a data recovery program and you don't get it all the first time, try tweaking the program you are using or try another program. Your data isn't going anywhere soon. Good Luck