HDD Issue help please

[Sho]

Im not sure what going on I have currently 7 HDD installed

2 SSD Crucial
3x1 Western digital black
1tb Hitach
Maxtor 320gb

One of the western drive are not turning on when i turn on pc, if i got to my computer show 6, have to restart few times it come back,
same in bios as well, or complete disappear middle of gaming or browsing or watching video.

Is it dieing? power issue

I74770k Not OC,16Gb corsair vengeance ram, asus maximus vi hero
GTX780 sli, not OC, Corsair Rm850 wat

Thanks in advance

 

[Surveyor]

Firstly I'd back up any data you need while you still have access.

Try using different power and data cables.

Also try connecting it to a different SATA port on the motherboard.