Computer crashed after plugging in external hard drive

I have an HP Desktop that I use for my home media server. I have one 500gb drive for Windows and a 6tb drive just for media storage. I added a bunch of movies to it and wanted to back it up. I plugged in my wd 3tb external and right away my computer becomes sluggish and unresponsive. I end up having to force restart. Usually during the boot process it shows my 2 hard drives. They are now coming up as not found. I reseated both drives and got it working. I tried the external drive again and same thing. Now reseating did not work a second time. Obviously my drive has crashed. But what are the odds that both drives would crash? I tried the external drive on a different computer and that worked fine. Both the 6tb drive and the external are less than 6 months old. Maybe just my 500gb drive crashesd? A few days we ago we had a really bad storm and the power was knocked out a total of 9 times. Annoyingly right when I would turn the computer back on it would go out again. Maybe that was the culprit? Anyways I can't see both drives failing at once. Maybe my board failed? Or let's say the 500gb drive failed would my 6tb not show up since it is just an installed drive for extra storage and doesn't have any OS on it?

Hp

Pegatron m2n78-la motherboard

AMD quad core 9750

8gb ram

Windows 7