You could try removing the drive from the enclosure and attaching it to an internal port and power supply. If it's just an enclosure problem that might work. Don't expect too much though, usually when portable hard drives don't work it means the disk itself is bad. There are several data recovery tools like this:http://www.gnu.org/software/ddrescue/ddrescue.html
There are expensive data recovery companies that will do it for you.