If information is really valuable, you have to bring your HDD to some big dara recovery company (big = they have class 100 clean room and licences from all HDD manufacturers). If there is no such a company in your area and if you do not have time to send your HDD to data recovery company, you can try online service at
http://binarybiz.com/hddrepair/index.html
It's unbelievable, but they can repair your HDD even if it cannot be detected by BIOS (and all other software just cannot see physical device on your system).