If the BIOS doesn't recognize the HD, it can't boot it... the possible solutions are:
1. Using a USB adapter/enclosure to try and access it from another computer so you can rescue personal files.
2. If the HD is not noisy, understanding that it's not damaged internally, it may be possible to make it run normally replacing the logical board with another from a same make and model HD.
3. Another possible solution is freezing the HD before attempting to acces or boot it... you should wrap it in cling wrap or in a plastic bag, and if possible vacuum it to extract excess air and the moisture in it...
4. Last resort is sending it to a HD Data Rescue Sevice if the data is that important.