I had an old PC with an Atom processor, two SATA hard disks with 40 GB and 160 GB each.
Recently I upgraded my PC, got a Gigabyte H61M DS2 Motherboard, 2 GB of RAM and Core I3 processor.
But whenever I connect the power connector to my 40 GB hard disk, the computer shows no sign of power. Even the CPU fan does not move.
Fortunatley, my OS is on the 160 GB disk and everything works fine if I disconnect the power connector from the 40 GB hardisk.