First off: How valuable is the data on the disk?
If this number is higher than $1000, stop fiddling and head to a professional recovery service. (Depending on your country)
If it is lower than $100, trash the disk, and buy a new one. You will never be able to trust the old disk again.
If the value is in between, follow these steps, until you give up because the time spent becomes more valuable than the contents of the disk:
Attach the disk to a 'puter. Check if the disk is visible in the BIOS settings.
If yes, boot any operating system, check the device manager list to see if the system sees the disk.
If yes, check the file system list (disk management console) if the device is listed there.
Sooo.. If you answered no to any of the question, you should go for help that is cheaper than the value of the data.
If the disk is available to the operating system, but not mounted, you need to have a tool to recover the lost data structures. Try google. Try computer magazines. If you can read german, try ct 20/2009 which had an excellent article.
There is an abundance of cheap data recovery software available, each of which may or may not help you.