How important/valuable is the disk's data to you? If highly, then you should only a approach a professional data recovery expert.
If not important, there are some DIY methods you can try for free. TestDisk is one example click here (download & instructions are lower down under 'Documentation'). It's not guaranteed to work, so use at your own risk. Also, remember that the more stuff you try on the drive, the harder it may become (even for a pro) to retrieve its data. G