Diagnose a Failing Hard Drive
By now there should be little question of the drive's health, but if there is and you value its contents you should start to back up the data. The problem with duplicating the data without the services of a data recovery specialist is that it will require you to power up the drive and have it spinning again, the time when it is most likely to die if the damage does prove to be mechanical.
There is no secret here except to keep your actions fast and efficient. Ideally you are going to want to copy the data to a source which is already connected to the computer and will require the least tinkering. An internal hard drive which in the computer would be ideal, but other options include an external hard drive, DVDs, to a NAS device, or a transfer over your network to another system. There is a definite chance the the drive could fail at any time so make sure to transfer what is most important first and if anything is truly important do not attempt this! If this is the case just power down, disconnect the drive and find a specialist. With any luck the drive will survive long enough to make the transfer. This will, in all likelihood, be the case because if the drive did not immediately die it has a fighting chance of surviving for a little bit more after the first signs of its failure.
There are not secrets to working with a failing hardrive, you just need to act quickly and decisively. The best plan of action is to always have a backup of data which you value.