I never hotplug/swap. I always shutdown.
And often just shutting down is not enough because the ATX Form Factor standard requires +5Vsb standby voltages be applied to several points across the motherboard when the computer is just "shutdown". Shutdown is not "off". It is really just in standby unless the power supply is unplugged from the wall, or, if it has one, the master power switch on the back of the power supply is switched to off or "0".
In the OP's defense, SATA drives are supposed to be hot-swappable. If you look at the image here:
...note how some of the pins are longer than others. Those are the hot-swappable pins intended to establish a common ground first. "
IN THEORY" if a cable connection is properly aligned when inserted, no damage or arcing (sparks) should occur. But that assumes the user is holding the connector straight, and the device connector and cable connector are in perfect condition.
HOWEVER, just because the SATA interface supports hot-swapping, that does not mean the device or the OS does. Most RAID controllers support hot-swapping, many plain motherboard SATA drive interfaces do not. And even if the device is hot-swappable, that does not ensure the OS will recognize it.
The ONLY time I hot-swap RAID drives is on a mission critical server - but I get nervous just thinking about it so I always try to schedule a downtime when possible so I can properly shutdown
and power off before disconnecting and connecting hardware. The exception is USB or eSATA connected devices.
@Garoxxar - if the connectors were properly aligned, you should never see any sparks - even if the device itself does not support hot-swapping. So you seeing sparks would suggest there is a short somewhere. The problem you have now is you don't know where and you risk damaging something else.
If me, I would install the suspect drive into an enclosure then hope and pray if the drive is damaged, the USB connection will isolate the short to the enclosure. I would not connect a drive that contains critical data to that motherboard.
That said, Jetster is right. "Hot-swapping" drives is no way to fix an OS, or even to determine if the OS on a drive is corrupt. Whoever led you down that trail needs to be smacked up side the head.