There is a second bay below the master HD.
Does this computer suppoort a second drive (for backup reasons)?
The main data cable has an additional plug at the end of it to use for the 2nd HD but there is no extra power cable.
What is needed here please
Also if it does support a second drive what settings are needed in the bios please?
You say, "The main data cable has an additional plug at the end of it to use for the 2nd HD but there is no extra power cable. " For SATA drives, the data cable has ONLY ONE connector on each end (total 2, not 3). The data cable is about ¾" wide and has 7 wires in it. What you describe sounds like you are looking at a 80-wire ribbon about 2¼" wide with connectors at both ends plus one in the middle. If that is so, you are looking at a IDE data cable, NOT SATA.
Now, your system specs say the mini-tower model has an empty spare bay for a HDD, and 4 SATA ports on the mobo, so you should be able to add a SATA HDD to the machine. To do that you will need a SATA data ribbon to connect to one of the mobo ports, and a SATA power connection from the PSU. This latter MAY be included already in the wires coming out of the PSU - it is a 15-pin connector, not like the 4-pin Molex heavy connector for older IDE devices. If you have one or more of these but not any spare ones, you can get a 2-from-1 adapter to create a spare. Otherwise you can get a different adapter to convert an unused 4-pin Molex to a SATA power connection.
If you actually have been looking at a IDE data ribbon and want to add another IDE HDD (rather than SATA), post here for a bit of advice on setting jumpers and which connectors to use. BUT if you go with a new SATA HDD, do NOT get tied up in setting jumpers for Master or Slave. There is NO such thing in SATA drives (they pertain only to IDE), and setting SATA jumpers wrong can cause trouble. Don't change the jumper on a SATA drive.