The fact that the OS doesn't detect the drive at all is not a good sign. Usually that means the drive controller has failed. TylerD75's suggestion about getting a USB (or eSata) docking bay to see if the system can access the data is not a bad one. I usually leave the drive in the system and boot a live Linux CD/DVD disc, or a Live USB thumb drive and see if Linux can access the device. If it can, then the controller is somewhat functional, and possibly only the file system is munged, which can often be restored to the point where you can at least get most of your data off of it.
This is BIOS not detecting the hdd. Of course, with the power off you first try replugging it a couple of times to clean the contacts, try with the plugs almost fully engaged to get a different contact area on the pins and sockets, try different mb sockets and power lines, and finally you try cooling it in the fridge and running it cold. Next step I think is feeling sad.
Does your BIOS detect other, similar drives?
TylerD75 seems a possability: how deep do I have to go for an icy box not knowing if it will work anyhow?
Rubberman: it's not the OS but the BIOS.
gerbil: I have 2 maxtors 500GB 1 is working fine the other has 2 partitions and refuses to be detected.
TylerD75 again: no BIOS settings have been changed, multiple connectors out/in did not work. The first partition was my OS Win 8.1. therefor I presume that this is the culprit and makes it impossible to enter the second partition.
But I figure that if your BIOS can't see it, any OS will probably not see it either.
Using an USB docking station has worked for me in the past, but it's a long shot, as disks tend to either work... or not. You could try to borrow one if you know anyone that might have one? Although they're not extreemly expensive, and I find them useful for backups (hint hint ;).
I have managed to rescue data from disks in the past, by continously rebooting the computer (or connecting then disconnecting a docking station). As sometimes the disk MIGHT start normally, but it will most certainly fail again (so expect it to die at any second).
If it were to start up normally, you should plan your copying carefully. Any copying might cause it to die permanently (most probably will, IF we're talking hardware failure). But as I said, I have done this in the past, and sometimes it has worked, other times not so much.
Just don't try to boot windows from the disk, as this may very well be the "reads" that push it over the edge.